<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019dac15-9f44-7693-b400-5589daf0ba5c,g:dabef6ea-4d96-4cf0-93c3-e695ac621787-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.optimum.com/role/CONSOLIDATEDBALANCESHEETS" xlink:type="simple" xlink:href="optu-20260331.xsd#CONSOLIDATEDBALANCESHEETS"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/CONSOLIDATEDBALANCESHEETS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dac15-a246-7233-9a39-f7f4849f095c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dac15-a246-75ec-8364-3cb3992f2642" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7233-9a39-f7f4849f095c" xlink:to="loc_us-gaap_StatementTable_019dac15-a246-75ec-8364-3cb3992f2642" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019dac15-a246-7a13-8f71-e01827f538c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-75ec-8364-3cb3992f2642" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019dac15-a246-7a13-8f71-e01827f538c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019dac15-a246-7a13-8f71-e01827f538c7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019dac15-a246-7a13-8f71-e01827f538c7" xlink:to="loc_us-gaap_ClassOfStockDomain_019dac15-a246-7a13-8f71-e01827f538c7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019dac15-a246-7d44-a942-228c6c6e1a71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019dac15-a246-7a13-8f71-e01827f538c7" xlink:to="loc_us-gaap_ClassOfStockDomain_019dac15-a246-7d44-a942-228c6c6e1a71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019dac15-a246-7071-9b4f-2113cf777253" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019dac15-a246-7d44-a942-228c6c6e1a71" xlink:to="loc_us-gaap_CommonClassAMember_019dac15-a246-7071-9b4f-2113cf777253" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019dac15-a246-7828-a080-5b82f2d59fe3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019dac15-a246-7d44-a942-228c6c6e1a71" xlink:to="loc_us-gaap_CommonClassBMember_019dac15-a246-7828-a080-5b82f2d59fe3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassCMember_019dac15-a246-7d71-ae07-80e8a95666c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019dac15-a246-7d44-a942-228c6c6e1a71" xlink:to="loc_us-gaap_CommonClassCMember_019dac15-a246-7d71-ae07-80e8a95666c3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_019dac15-a246-7c10-886f-55d36b1832e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7233-9a39-f7f4849f095c" xlink:to="loc_us-gaap_AssetsAbstract_019dac15-a246-7c10-886f-55d36b1832e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_019dac15-a246-7126-b010-b657ce72fcae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7c10-886f-55d36b1832e5" xlink:to="loc_us-gaap_AssetsCurrentAbstract_019dac15-a246-7126-b010-b657ce72fcae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dac15-a246-7454-9966-f7f95c5f51f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dac15-a246-7126-b010-b657ce72fcae" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dac15-a246-7454-9966-f7f95c5f51f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashCurrent_019dac15-a246-7ba2-9023-0f4e587ed2f0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dac15-a246-7126-b010-b657ce72fcae" xlink:to="loc_us-gaap_RestrictedCashCurrent_019dac15-a246-7ba2-9023-0f4e587ed2f0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019dac15-a246-7e58-a029-f2d1e4e6a0f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dac15-a246-7126-b010-b657ce72fcae" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019dac15-a246-7e58-a029-f2d1e4e6a0f2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019dac15-a246-7101-bbd8-c44ad54b4985" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dac15-a246-7126-b010-b657ce72fcae" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019dac15-a246-7101-bbd8-c44ad54b4985" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_019dac15-a246-7fb6-b90a-73b397796cd8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dac15-a246-7126-b010-b657ce72fcae" xlink:to="loc_us-gaap_AssetsCurrent_019dac15-a246-7fb6-b90a-73b397796cd8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019dac15-a246-748d-a922-7ce405b09456" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7c10-886f-55d36b1832e5" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019dac15-a246-748d-a922-7ce405b09456" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_019dac15-a246-7f96-a4aa-e35040ef07c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7c10-886f-55d36b1832e5" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_019dac15-a246-7f96-a4aa-e35040ef07c7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_019dac15-a246-7a67-a6b6-1a2eea26e576" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7c10-886f-55d36b1832e5" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_019dac15-a246-7a67-a6b6-1a2eea26e576" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019dac15-a246-7c26-b213-a0727d8978f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7c10-886f-55d36b1832e5" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019dac15-a246-7c26-b213-a0727d8978f5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_019dac15-a246-78c2-aa3d-65ffb66be35f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7c10-886f-55d36b1832e5" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_019dac15-a246-78c2-aa3d-65ffb66be35f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019dac15-a246-707d-af30-96494df4ff1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7c10-886f-55d36b1832e5" xlink:to="loc_us-gaap_Goodwill_019dac15-a246-707d-af30-96494df4ff1d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019dac15-a246-7395-9cbe-7bffe9fafa6c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7c10-886f-55d36b1832e5" xlink:to="loc_us-gaap_Assets_019dac15-a246-7395-9cbe-7bffe9fafa6c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-736b-80f9-0d3f09e2801f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7233-9a39-f7f4849f095c" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-736b-80f9-0d3f09e2801f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-72bf-b377-b50b8ba352a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-736b-80f9-0d3f09e2801f" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-72bf-b377-b50b8ba352a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_019dac15-a246-769c-a460-50a5a15ed5cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-72bf-b377-b50b8ba352a3" xlink:to="loc_us-gaap_AccountsPayableCurrent_019dac15-a246-769c-a460-50a5a15ed5cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPayableCurrent_019dac15-a246-7d44-bd72-a2c82be2c563" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-72bf-b377-b50b8ba352a3" xlink:to="loc_us-gaap_InterestPayableCurrent_019dac15-a246-7d44-bd72-a2c82be2c563" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_019dac15-a246-708a-9c4f-456943b6e34c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-72bf-b377-b50b8ba352a3" xlink:to="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_019dac15-a246-708a-9c4f-456943b6e34c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019dac15-a246-7630-8bb6-90b375025029" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-72bf-b377-b50b8ba352a3" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019dac15-a246-7630-8bb6-90b375025029" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_019dac15-a246-788f-81f6-7623d2152c4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-72bf-b377-b50b8ba352a3" xlink:to="loc_us-gaap_LongTermDebtCurrent_019dac15-a246-788f-81f6-7623d2152c4f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesCurrent_019dac15-a246-7658-9281-ebfa53ba7112" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-72bf-b377-b50b8ba352a3" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesCurrent_019dac15-a246-7658-9281-ebfa53ba7112" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_019dac15-a246-7497-b984-bced5304cd36" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-72bf-b377-b50b8ba352a3" xlink:to="loc_us-gaap_LiabilitiesCurrent_019dac15-a246-7497-b984-bced5304cd36" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_019dac15-a246-7af0-9908-50a553575a2a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-736b-80f9-0d3f09e2801f" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_019dac15-a246-7af0-9908-50a553575a2a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019dac15-a246-7052-82e7-addd14f362cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-736b-80f9-0d3f09e2801f" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019dac15-a246-7052-82e7-addd14f362cf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019dac15-a246-71e0-951e-9e76a5a04a6f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-736b-80f9-0d3f09e2801f" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019dac15-a246-71e0-951e-9e76a5a04a6f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019dac15-a246-79ac-a683-67ace699e071" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-736b-80f9-0d3f09e2801f" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019dac15-a246-79ac-a683-67ace699e071" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019dac15-a246-70a0-a45f-0763f00d688b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-736b-80f9-0d3f09e2801f" xlink:to="loc_us-gaap_Liabilities_019dac15-a246-70a0-a45f-0763f00d688b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_019dac15-a246-7654-b145-cef39310e10a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-736b-80f9-0d3f09e2801f" xlink:to="loc_us-gaap_CommitmentsAndContingencies_019dac15-a246-7654-b145-cef39310e10a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-798c-b4eb-bfa88f2be107" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-736b-80f9-0d3f09e2801f" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-798c-b4eb-bfa88f2be107" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockValue_019dac15-a246-70a5-b89f-ab14c0b40b79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-798c-b4eb-bfa88f2be107" xlink:to="loc_us-gaap_PreferredStockValue_019dac15-a246-70a5-b89f-ab14c0b40b79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019dac15-a246-7bc6-8f5d-4bf40134c4dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-798c-b4eb-bfa88f2be107" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019dac15-a246-7bc6-8f5d-4bf40134c4dd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019dac15-a246-7569-90ec-624551156199" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-798c-b4eb-bfa88f2be107" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019dac15-a246-7569-90ec-624551156199" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019dac15-a246-7a46-9155-adbe0085c2fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-798c-b4eb-bfa88f2be107" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019dac15-a246-7a46-9155-adbe0085c2fa" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_019dac15-a246-7090-9b92-ab498d6ec667" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-798c-b4eb-bfa88f2be107" xlink:to="loc_us-gaap_SharesIssued_019dac15-a246-7090-9b92-ab498d6ec667" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_019dac15-a246-7584-89d9-d77b5bc1ac9c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-798c-b4eb-bfa88f2be107" xlink:to="loc_us-gaap_CommonStockValue_019dac15-a246-7584-89d9-d77b5bc1ac9c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapital_019dac15-a246-70ef-89b0-6b6908fceab8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-798c-b4eb-bfa88f2be107" xlink:to="loc_us-gaap_AdditionalPaidInCapital_019dac15-a246-70ef-89b0-6b6908fceab8" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019dac15-a246-7d1f-a4be-89263c5a348e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-798c-b4eb-bfa88f2be107" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019dac15-a246-7d1f-a4be-89263c5a348e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_TotalStockholdersEquityBeforeAccumulatedOtherComprehensiveIncomeLossandNoncontrollingInterest_019dac15-a246-7de1-bff8-99f75db4253f" xlink:href="optu-20260331.xsd#optu_TotalStockholdersEquityBeforeAccumulatedOtherComprehensiveIncomeLossandNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-798c-b4eb-bfa88f2be107" xlink:to="loc_optu_TotalStockholdersEquityBeforeAccumulatedOtherComprehensiveIncomeLossandNoncontrollingInterest_019dac15-a246-7de1-bff8-99f75db4253f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonValue_019dac15-a246-7e4a-93c1-c71465cc1a76" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-798c-b4eb-bfa88f2be107" xlink:to="loc_us-gaap_TreasuryStockCommonValue_019dac15-a246-7e4a-93c1-c71465cc1a76" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_019dac15-a246-7db7-a268-b61f2d4d6789" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-798c-b4eb-bfa88f2be107" xlink:to="loc_us-gaap_TreasuryStockCommonShares_019dac15-a246-7db7-a268-b61f2d4d6789" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dac15-a246-78b0-b7a5-9569dc05e702" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-798c-b4eb-bfa88f2be107" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dac15-a246-78b0-b7a5-9569dc05e702" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019dac15-a246-78b7-adb7-33c4fa8db6ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-798c-b4eb-bfa88f2be107" xlink:to="loc_us-gaap_StockholdersEquity_019dac15-a246-78b7-adb7-33c4fa8db6ee" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterest_019dac15-a246-79fb-acfc-53aff0bc4b3b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-798c-b4eb-bfa88f2be107" xlink:to="loc_us-gaap_MinorityInterest_019dac15-a246-79fb-acfc-53aff0bc4b3b" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019dac15-a246-7bff-9026-cb2034afa206" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-798c-b4eb-bfa88f2be107" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019dac15-a246-7bff-9026-cb2034afa206" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_019dac15-a246-7e53-904f-03e97a1432f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-736b-80f9-0d3f09e2801f" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_019dac15-a246-7e53-904f-03e97a1432f3" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/CONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="simple" xlink:href="optu-20260331.xsd#CONSOLIDATEDBALANCESHEETSParenthetical"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/CONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dac15-a246-7f87-b878-d89ff48eeffc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dac15-a246-73de-80d5-07b8a50f5adb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7f87-b878-d89ff48eeffc" xlink:to="loc_us-gaap_StatementTable_019dac15-a246-73de-80d5-07b8a50f5adb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-7052-82d3-b1940cd98fa1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-73de-80d5-07b8a50f5adb" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-7052-82d3-b1940cd98fa1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a246-7052-82d3-b1940cd98fa1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-7052-82d3-b1940cd98fa1" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a246-7052-82d3-b1940cd98fa1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a246-79d4-ab38-7e37148ed044" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-7052-82d3-b1940cd98fa1" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a246-79d4-ab38-7e37148ed044" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dac15-a246-7fe4-9feb-90e1b0ad3f86" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019dac15-a246-79d4-ab38-7e37148ed044" xlink:to="loc_us-gaap_RelatedPartyMember_019dac15-a246-7fe4-9feb-90e1b0ad3f86" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019dac15-a246-7d68-bf34-34e9090cd0e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-73de-80d5-07b8a50f5adb" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019dac15-a246-7d68-bf34-34e9090cd0e8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019dac15-a246-7d68-bf34-34e9090cd0e8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019dac15-a246-7d68-bf34-34e9090cd0e8" xlink:to="loc_us-gaap_ClassOfStockDomain_019dac15-a246-7d68-bf34-34e9090cd0e8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019dac15-a246-79cb-8670-976e6d6957a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019dac15-a246-7d68-bf34-34e9090cd0e8" xlink:to="loc_us-gaap_ClassOfStockDomain_019dac15-a246-79cb-8670-976e6d6957a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019dac15-a246-7fc0-9e44-23d062ad517c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019dac15-a246-79cb-8670-976e6d6957a1" xlink:to="loc_us-gaap_CommonClassAMember_019dac15-a246-7fc0-9e44-23d062ad517c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019dac15-a246-789b-94e8-2191ec36924c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019dac15-a246-79cb-8670-976e6d6957a1" xlink:to="loc_us-gaap_CommonClassBMember_019dac15-a246-789b-94e8-2191ec36924c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassCMember_019dac15-a246-759b-a190-7e0339941eb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019dac15-a246-79cb-8670-976e6d6957a1" xlink:to="loc_us-gaap_CommonClassCMember_019dac15-a246-759b-a190-7e0339941eb8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_019dac15-a246-7458-b365-6599101f196c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7f87-b878-d89ff48eeffc" xlink:to="loc_us-gaap_AssetsAbstract_019dac15-a246-7458-b365-6599101f196c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019dac15-a246-7c6e-b281-67bf21ed35da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7458-b365-6599101f196c" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019dac15-a246-7c6e-b281-67bf21ed35da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019dac15-a246-7fd0-b013-b2f26cb5bfe1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7458-b365-6599101f196c" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019dac15-a246-7fd0-b013-b2f26cb5bfe1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019dac15-a246-70a8-bf4a-d8b549dd7647" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7458-b365-6599101f196c" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019dac15-a246-70a8-bf4a-d8b549dd7647" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019dac15-a246-7427-aca0-6ddbda04a5d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7458-b365-6599101f196c" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019dac15-a246-7427-aca0-6ddbda04a5d7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-7210-9c59-d6baae1b950b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7f87-b878-d89ff48eeffc" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-7210-9c59-d6baae1b950b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesCurrent_019dac15-a246-7450-a093-756e2df76928" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-7210-9c59-d6baae1b950b" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesCurrent_019dac15-a246-7450-a093-756e2df76928" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-773e-8de3-0f9987b601dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-7210-9c59-d6baae1b950b" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-773e-8de3-0f9987b601dc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019dac15-a246-7104-9cf0-a9012f87f993" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-773e-8de3-0f9987b601dc" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019dac15-a246-7104-9cf0-a9012f87f993" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_019dac15-a246-7176-b126-d0b2312dcae3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-773e-8de3-0f9987b601dc" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_019dac15-a246-7176-b126-d0b2312dcae3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_019dac15-a246-7d41-9d93-928fdf496f60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-773e-8de3-0f9987b601dc" xlink:to="loc_us-gaap_PreferredStockSharesIssued_019dac15-a246-7d41-9d93-928fdf496f60" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_019dac15-a246-7bf5-a7e4-4f1de53da614" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-773e-8de3-0f9987b601dc" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_019dac15-a246-7bf5-a7e4-4f1de53da614" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019dac15-a246-71f5-9ef5-5182da3004fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-773e-8de3-0f9987b601dc" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019dac15-a246-71f5-9ef5-5182da3004fa" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019dac15-a246-7c3e-8589-2569585f79a7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-773e-8de3-0f9987b601dc" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019dac15-a246-7c3e-8589-2569585f79a7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019dac15-a246-7a9b-9741-b08cf4a5cd2c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-773e-8de3-0f9987b601dc" xlink:to="loc_us-gaap_CommonStockSharesIssued_019dac15-a246-7a9b-9741-b08cf4a5cd2c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019dac15-a246-742e-ac23-a1f351925abb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-773e-8de3-0f9987b601dc" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019dac15-a246-742e-ac23-a1f351925abb" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_019dac15-a246-79fd-8410-b8ffdb1678a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dac15-a246-773e-8de3-0f9987b601dc" xlink:to="loc_us-gaap_TreasuryStockCommonShares_019dac15-a246-79fd-8410-b8ffdb1678a3" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/CONSOLIDATEDSTATEMENTSOFOPERATIONSParenthetical" xlink:type="simple" xlink:href="optu-20260331.xsd#CONSOLIDATEDSTATEMENTSOFOPERATIONSParenthetical"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/CONSOLIDATEDSTATEMENTSOFOPERATIONSParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dac15-a246-7ad3-8773-4f529fe7d682" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dac15-a246-7452-9d66-0ef881311d06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7ad3-8773-4f529fe7d682" xlink:to="loc_us-gaap_StatementTable_019dac15-a246-7452-9d66-0ef881311d06" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a246-780b-a771-0239c5091bf9" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-7452-9d66-0ef881311d06" xlink:to="loc_dei_LegalEntityAxis_019dac15-a246-780b-a771-0239c5091bf9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-780b-a771-0239c5091bf9_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-780b-a771-0239c5091bf9" xlink:to="loc_dei_EntityDomain_019dac15-a246-780b-a771-0239c5091bf9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-702c-892b-e3be4823e953" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-780b-a771-0239c5091bf9" xlink:to="loc_dei_EntityDomain_019dac15-a246-702c-892b-e3be4823e953" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsMember_019dac15-a246-70b8-9ff3-243775c1081f" xlink:href="optu-20260331.xsd#optu_CSCHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a246-702c-892b-e3be4823e953" xlink:to="loc_optu_CSCHoldingsMember_019dac15-a246-70b8-9ff3-243775c1081f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-7d4b-90a5-dfd2aec8c65d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-7452-9d66-0ef881311d06" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-7d4b-90a5-dfd2aec8c65d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a246-7d4b-90a5-dfd2aec8c65d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-7d4b-90a5-dfd2aec8c65d" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a246-7d4b-90a5-dfd2aec8c65d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a246-76e1-adf8-71f08554444a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-7d4b-90a5-dfd2aec8c65d" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a246-76e1-adf8-71f08554444a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dac15-a246-7b11-80fc-1d669348aa6c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019dac15-a246-76e1-adf8-71f08554444a" xlink:to="loc_us-gaap_RelatedPartyMember_019dac15-a246-7b11-80fc-1d669348aa6c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019dac15-a246-7a62-a6a1-8819972193b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7ad3-8773-4f529fe7d682" xlink:to="loc_us-gaap_Revenues_019dac15-a246-7a62-a6a1-8819972193b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_019dac15-a246-7cd6-9187-b167fb766c53" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7ad3-8773-4f529fe7d682" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_019dac15-a246-7cd6-9187-b167fb766c53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCostAndExpenseOperating_019dac15-a246-74e0-b977-db6fdffd78be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCostAndExpenseOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7ad3-8773-4f529fe7d682" xlink:to="loc_us-gaap_OtherCostAndExpenseOperating_019dac15-a246-74e0-b977-db6fdffd78be" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_019dac15-a246-782d-931d-411b57f705e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7ad3-8773-4f529fe7d682" xlink:to="loc_us-gaap_EarningsPerShareDiluted_019dac15-a246-782d-931d-411b57f705e1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019dac15-a246-710c-acfa-7dce723fc5f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7ad3-8773-4f529fe7d682" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019dac15-a246-710c-acfa-7dce723fc5f8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019dac15-a246-778a-ada0-a6fe339323d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7ad3-8773-4f529fe7d682" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019dac15-a246-778a-ada0-a6fe339323d9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_019dac15-a246-7bb1-ab1f-64f31a6a2ecf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7ad3-8773-4f529fe7d682" xlink:to="loc_us-gaap_EarningsPerShareBasic_019dac15-a246-7bb1-ab1f-64f31a6a2ecf" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/CONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="simple" xlink:href="optu-20260331.xsd#CONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/CONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dac15-a246-7c5a-bbce-6d990ed81e5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dac15-a246-732a-b1b9-6ee3220a4b2d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7c5a-bbce-6d990ed81e5d" xlink:to="loc_us-gaap_StatementTable_019dac15-a246-732a-b1b9-6ee3220a4b2d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019dac15-a246-707a-ad99-da8fd5dc4304" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-732a-b1b9-6ee3220a4b2d" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019dac15-a246-707a-ad99-da8fd5dc4304" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019dac15-a246-707a-ad99-da8fd5dc4304_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019dac15-a246-707a-ad99-da8fd5dc4304" xlink:to="loc_us-gaap_ClassOfStockDomain_019dac15-a246-707a-ad99-da8fd5dc4304_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019dac15-a246-78cb-8874-13a8280fd68b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019dac15-a246-707a-ad99-da8fd5dc4304" xlink:to="loc_us-gaap_ClassOfStockDomain_019dac15-a246-78cb-8874-13a8280fd68b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019dac15-a246-79c4-a6ce-8f81b1cc3507" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019dac15-a246-78cb-8874-13a8280fd68b" xlink:to="loc_us-gaap_CommonClassAMember_019dac15-a246-79c4-a6ce-8f81b1cc3507" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019dac15-a246-7378-8288-47e3274717d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019dac15-a246-78cb-8874-13a8280fd68b" xlink:to="loc_us-gaap_CommonClassBMember_019dac15-a246-7378-8288-47e3274717d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019dac15-a246-7e4b-882c-52689db887c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-732a-b1b9-6ee3220a4b2d" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019dac15-a246-7e4b-882c-52689db887c0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dac15-a246-7e4b-882c-52689db887c0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dac15-a246-7e4b-882c-52689db887c0" xlink:to="loc_us-gaap_EquityComponentDomain_019dac15-a246-7e4b-882c-52689db887c0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dac15-a246-7869-aa76-a5f4b798d1cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dac15-a246-7e4b-882c-52689db887c0" xlink:to="loc_us-gaap_EquityComponentDomain_019dac15-a246-7869-aa76-a5f4b798d1cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParentMember_019dac15-a246-7dd2-9a3b-5c530ad9ccc9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dac15-a246-7869-aa76-a5f4b798d1cf" xlink:to="loc_us-gaap_ParentMember_019dac15-a246-7dd2-9a3b-5c530ad9ccc9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019dac15-a246-7783-8cf3-1a594b976b87" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019dac15-a246-7dd2-9a3b-5c530ad9ccc9" xlink:to="loc_us-gaap_CommonStockMember_019dac15-a246-7783-8cf3-1a594b976b87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019dac15-a246-713b-9716-e971dd2c4dfd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019dac15-a246-7dd2-9a3b-5c530ad9ccc9" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019dac15-a246-713b-9716-e971dd2c4dfd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019dac15-a246-76e3-84c2-2a8550738632" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019dac15-a246-7dd2-9a3b-5c530ad9ccc9" xlink:to="loc_us-gaap_RetainedEarningsMember_019dac15-a246-76e3-84c2-2a8550738632" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_019dac15-a246-77e8-b202-d33dc10f4cc3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019dac15-a246-7dd2-9a3b-5c530ad9ccc9" xlink:to="loc_us-gaap_TreasuryStockCommonMember_019dac15-a246-77e8-b202-d33dc10f4cc3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dac15-a246-7f96-b1be-66049343c027" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019dac15-a246-7dd2-9a3b-5c530ad9ccc9" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dac15-a246-7f96-b1be-66049343c027" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_019dac15-a246-7902-8efe-ce569c2ae61d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dac15-a246-7869-aa76-a5f4b798d1cf" xlink:to="loc_us-gaap_NoncontrollingInterestMember_019dac15-a246-7902-8efe-ce569c2ae61d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a246-7362-affb-4257b796a1e8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-732a-b1b9-6ee3220a4b2d" xlink:to="loc_dei_LegalEntityAxis_019dac15-a246-7362-affb-4257b796a1e8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-7362-affb-4257b796a1e8_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-7362-affb-4257b796a1e8" xlink:to="loc_dei_EntityDomain_019dac15-a246-7362-affb-4257b796a1e8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-7845-80ac-8fbfc402762e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-7362-affb-4257b796a1e8" xlink:to="loc_dei_EntityDomain_019dac15-a246-7845-80ac-8fbfc402762e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsMember_019dac15-a246-77fb-bf3b-c1b05ce7c48e" xlink:href="optu-20260331.xsd#optu_CSCHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a246-7845-80ac-8fbfc402762e" xlink:to="loc_optu_CSCHoldingsMember_019dac15-a246-77fb-bf3b-c1b05ce7c48e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-7d51-8dba-7a8e335c709b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7c5a-bbce-6d990ed81e5d" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-7d51-8dba-7a8e335c709b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019dac15-a246-74ef-a0f8-7388dd825f29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-7d51-8dba-7a8e335c709b" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019dac15-a246-74ef-a0f8-7388dd825f29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019dac15-a246-7cd4-87ee-055f0c9fe583" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-7d51-8dba-7a8e335c709b" xlink:to="loc_us-gaap_NetIncomeLoss_019dac15-a246-7cd4-87ee-055f0c9fe583" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_019dac15-a246-71dd-a309-157f3456116d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-7d51-8dba-7a8e335c709b" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_019dac15-a246-71dd-a309-157f3456116d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_019dac15-a246-72c7-80a1-f8d9f42d196d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-7d51-8dba-7a8e335c709b" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_019dac15-a246-72c7-80a1-f8d9f42d196d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_019dac15-a246-750e-a6d7-297875f391a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-7d51-8dba-7a8e335c709b" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_019dac15-a246-750e-a6d7-297875f391a6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019dac15-a246-7fba-9c28-1f6ee8779c8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-7d51-8dba-7a8e335c709b" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019dac15-a246-7fba-9c28-1f6ee8779c8a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_019dac15-a246-711f-bb72-8be64da0a150" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-7d51-8dba-7a8e335c709b" xlink:to="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_019dac15-a246-711f-bb72-8be64da0a150" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_OtherAdjustmentToEquityDeficiency_019dac15-a246-7c15-8cef-06d75c5d73f2" xlink:href="optu-20260331.xsd#optu_OtherAdjustmentToEquityDeficiency"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-7d51-8dba-7a8e335c709b" xlink:to="loc_optu_OtherAdjustmentToEquityDeficiency_019dac15-a246-7c15-8cef-06d75c5d73f2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019dac15-a246-7c3f-a02e-c252ced4334f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCash_019dac15-a246-73b3-b860-b0fed3a22f44" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-7d51-8dba-7a8e335c709b" xlink:to="loc_us-gaap_DividendsCash_019dac15-a246-73b3-b860-b0fed3a22f44" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityOther_019dac15-a246-720c-bb88-58e4b063856e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-7d51-8dba-7a8e335c709b" xlink:to="loc_us-gaap_StockholdersEquityOther_019dac15-a246-720c-bb88-58e4b063856e" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_019dac15-a246-7a3d-a27a-790c8d7c134c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7c5a-bbce-6d990ed81e5d" xlink:to="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_019dac15-a246-7a3d-a27a-790c8d7c134c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_DistributionMadeToAnEntityUnderCommonControl_019de398-2663-7cb4-a345-25c3c36e4a38" xlink:href="optu-20260331.xsd#optu_DistributionMadeToAnEntityUnderCommonControl"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7c5a-bbce-6d990ed81e5d" xlink:to="loc_optu_DistributionMadeToAnEntityUnderCommonControl_019de398-2663-7cb4-a345-25c3c36e4a38" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/CSCHOLDINGSCONSOLIDATEDBALANCESHEETS" xlink:type="simple" xlink:href="optu-20260331.xsd#CSCHOLDINGSCONSOLIDATEDBALANCESHEETS"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/CSCHOLDINGSCONSOLIDATEDBALANCESHEETS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dac15-a246-7e62-a610-8851411cf752" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dac15-a246-78d1-a7b2-b4ddd952a58c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7e62-a610-8851411cf752" xlink:to="loc_us-gaap_StatementTable_019dac15-a246-78d1-a7b2-b4ddd952a58c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a246-7c7d-ac6b-f9331376a0a2" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-78d1-a7b2-b4ddd952a58c" xlink:to="loc_dei_LegalEntityAxis_019dac15-a246-7c7d-ac6b-f9331376a0a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-7c7d-ac6b-f9331376a0a2_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-7c7d-ac6b-f9331376a0a2" xlink:to="loc_dei_EntityDomain_019dac15-a246-7c7d-ac6b-f9331376a0a2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-7545-89a2-645290d64106" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-7c7d-ac6b-f9331376a0a2" xlink:to="loc_dei_EntityDomain_019dac15-a246-7545-89a2-645290d64106" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsMember_019dac15-a246-7340-b775-7cb7094279e1" xlink:href="optu-20260331.xsd#optu_CSCHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a246-7545-89a2-645290d64106" xlink:to="loc_optu_CSCHoldingsMember_019dac15-a246-7340-b775-7cb7094279e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-74b4-b7ee-0961cc9e595f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-78d1-a7b2-b4ddd952a58c" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-74b4-b7ee-0961cc9e595f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a246-74b4-b7ee-0961cc9e595f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-74b4-b7ee-0961cc9e595f" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a246-74b4-b7ee-0961cc9e595f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a246-79d4-840b-07ac7e00d2ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-74b4-b7ee-0961cc9e595f" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a246-79d4-840b-07ac7e00d2ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dac15-a246-7e88-a250-1fd6bb8a9484" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019dac15-a246-79d4-840b-07ac7e00d2ce" xlink:to="loc_us-gaap_RelatedPartyMember_019dac15-a246-7e88-a250-1fd6bb8a9484" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_019dac15-a246-7e4a-9275-c315d7aca32d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7e62-a610-8851411cf752" xlink:to="loc_us-gaap_AssetsAbstract_019dac15-a246-7e4a-9275-c315d7aca32d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_019dac15-a246-75a1-a89c-f16685963ab3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7e4a-9275-c315d7aca32d" xlink:to="loc_us-gaap_AssetsCurrentAbstract_019dac15-a246-75a1-a89c-f16685963ab3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dac15-a246-7e79-8f11-d822b84b8357" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dac15-a246-75a1-a89c-f16685963ab3" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dac15-a246-7e79-8f11-d822b84b8357" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashCurrent_019dac15-a246-7f55-8590-7d2e1ffc75ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dac15-a246-75a1-a89c-f16685963ab3" xlink:to="loc_us-gaap_RestrictedCashCurrent_019dac15-a246-7f55-8590-7d2e1ffc75ba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019dac15-a246-7afe-aa04-a8eac83d8afd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dac15-a246-75a1-a89c-f16685963ab3" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019dac15-a246-7afe-aa04-a8eac83d8afd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019dac15-a246-796a-9bf1-5e49fea5bceb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dac15-a246-75a1-a89c-f16685963ab3" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019dac15-a246-796a-9bf1-5e49fea5bceb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_019dac15-a246-7974-ad28-ccb2c1f02158" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dac15-a246-75a1-a89c-f16685963ab3" xlink:to="loc_us-gaap_AssetsCurrent_019dac15-a246-7974-ad28-ccb2c1f02158" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019dac15-a246-7203-83ea-e7e3e5f513ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7e4a-9275-c315d7aca32d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019dac15-a246-7203-83ea-e7e3e5f513ed" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_019dac15-a246-7886-9a50-af3b37099a75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7e4a-9275-c315d7aca32d" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_019dac15-a246-7886-9a50-af3b37099a75" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_019dac15-a246-76cd-b250-5dfede483080" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7e4a-9275-c315d7aca32d" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_019dac15-a246-76cd-b250-5dfede483080" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019dac15-a246-7616-b9d2-4fea297b2ed5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7e4a-9275-c315d7aca32d" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019dac15-a246-7616-b9d2-4fea297b2ed5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_019dac15-a246-73ef-9185-be3de959b554" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7e4a-9275-c315d7aca32d" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_019dac15-a246-73ef-9185-be3de959b554" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019dac15-a246-7991-a6b5-01c9e436493f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7e4a-9275-c315d7aca32d" xlink:to="loc_us-gaap_Goodwill_019dac15-a246-7991-a6b5-01c9e436493f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019dac15-a246-709a-a4ad-cfe52b1205ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dac15-a246-7e4a-9275-c315d7aca32d" xlink:to="loc_us-gaap_Assets_019dac15-a246-709a-a4ad-cfe52b1205ff" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-7207-8b97-09118291423c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7e62-a610-8851411cf752" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-7207-8b97-09118291423c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-7f10-98d8-f2803fa11bd9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-7207-8b97-09118291423c" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-7f10-98d8-f2803fa11bd9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_019dac15-a246-77c6-8f0e-88ac76c06684" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-7f10-98d8-f2803fa11bd9" xlink:to="loc_us-gaap_AccountsPayableCurrent_019dac15-a246-77c6-8f0e-88ac76c06684" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPayableCurrent_019dac15-a246-7a94-8798-05194a182aa7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-7f10-98d8-f2803fa11bd9" xlink:to="loc_us-gaap_InterestPayableCurrent_019dac15-a246-7a94-8798-05194a182aa7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_019dac15-a246-776f-b9aa-e71a93231b28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-7f10-98d8-f2803fa11bd9" xlink:to="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_019dac15-a246-776f-b9aa-e71a93231b28" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019dac15-a246-71e7-ac09-2bb6d47dd530" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-7f10-98d8-f2803fa11bd9" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019dac15-a246-71e7-ac09-2bb6d47dd530" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayable_019dac15-a246-7821-a56e-921e9705daf1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-7f10-98d8-f2803fa11bd9" xlink:to="loc_us-gaap_NotesPayable_019dac15-a246-7821-a56e-921e9705daf1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_019dac15-a246-7bc0-8d52-cd464a4c9cfb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-7f10-98d8-f2803fa11bd9" xlink:to="loc_us-gaap_LongTermDebtCurrent_019dac15-a246-7bc0-8d52-cd464a4c9cfb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesCurrent_019dac15-a246-7b33-bd38-253462630b60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-7f10-98d8-f2803fa11bd9" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesCurrent_019dac15-a246-7b33-bd38-253462630b60" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_019dac15-a246-78aa-bba1-fc7eac5b4576" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dac15-a246-7f10-98d8-f2803fa11bd9" xlink:to="loc_us-gaap_LiabilitiesCurrent_019dac15-a246-78aa-bba1-fc7eac5b4576" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_019dac15-a246-7289-8d8e-6ad76371a071" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-7207-8b97-09118291423c" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_019dac15-a246-7289-8d8e-6ad76371a071" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019dac15-a246-77db-b130-af64ca08a2d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-7207-8b97-09118291423c" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019dac15-a246-77db-b130-af64ca08a2d3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019dac15-a246-7d66-bd27-d28128cd5a8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-7207-8b97-09118291423c" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019dac15-a246-7d66-bd27-d28128cd5a8e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019dac15-a246-722a-bc3f-6ec4f000becd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-7207-8b97-09118291423c" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019dac15-a246-722a-bc3f-6ec4f000becd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019dac15-a246-7ebd-abfe-abdc2815b7d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-7207-8b97-09118291423c" xlink:to="loc_us-gaap_Liabilities_019dac15-a246-7ebd-abfe-abdc2815b7d6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_019dac15-a246-75bd-ad4b-157ab161fbb1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-7207-8b97-09118291423c" xlink:to="loc_us-gaap_CommitmentsAndContingencies_019dac15-a246-75bd-ad4b-157ab161fbb1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedLiabilityCompanyLLCMembersEquityAbstract_019dac15-a246-7d4a-9da3-370e6556a697" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LimitedLiabilityCompanyLLCMembersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-7207-8b97-09118291423c" xlink:to="loc_us-gaap_LimitedLiabilityCompanyLLCMembersEquityAbstract_019dac15-a246-7d4a-9da3-370e6556a697" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_Membershipinterestbeforeaccumulatedcomprehensiveloss_019dac15-a246-76e9-9c2d-f460d2ddf0f5" xlink:href="optu-20260331.xsd#optu_Membershipinterestbeforeaccumulatedcomprehensiveloss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LimitedLiabilityCompanyLLCMembersEquityAbstract_019dac15-a246-7d4a-9da3-370e6556a697" xlink:to="loc_optu_Membershipinterestbeforeaccumulatedcomprehensiveloss_019dac15-a246-76e9-9c2d-f460d2ddf0f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dac15-a246-7e5d-9290-497841366437" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LimitedLiabilityCompanyLLCMembersEquityAbstract_019dac15-a246-7d4a-9da3-370e6556a697" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dac15-a246-7e5d-9290-497841366437" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MembersEquity_019dac15-a246-7361-ae36-f16890da76da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MembersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LimitedLiabilityCompanyLLCMembersEquityAbstract_019dac15-a246-7d4a-9da3-370e6556a697" xlink:to="loc_us-gaap_MembersEquity_019dac15-a246-7361-ae36-f16890da76da" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterest_019dac15-a246-7f73-a5aa-fae48e8bc0f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LimitedLiabilityCompanyLLCMembersEquityAbstract_019dac15-a246-7d4a-9da3-370e6556a697" xlink:to="loc_us-gaap_MinorityInterest_019dac15-a246-7f73-a5aa-fae48e8bc0f8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_019dac15-a246-70fb-bdf7-6ca0fecfcbb4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LimitedLiabilityCompanyLLCMembersEquityAbstract_019dac15-a246-7d4a-9da3-370e6556a697" xlink:to="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_019dac15-a246-70fb-bdf7-6ca0fecfcbb4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_019dac15-a246-7fd2-9671-fbb88bb99cb4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dac15-a246-7207-8b97-09118291423c" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_019dac15-a246-7fd2-9671-fbb88bb99cb4" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/CSCHOLDINGSCONSOLIDATEDBALANCESHEETSParentheticals" xlink:type="simple" xlink:href="optu-20260331.xsd#CSCHOLDINGSCONSOLIDATEDBALANCESHEETSParentheticals"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/CSCHOLDINGSCONSOLIDATEDBALANCESHEETSParentheticals" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dac15-a246-7d22-a7ad-50153bf6d950" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dac15-a246-7c71-b3e2-c3fb8ba7f9b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7d22-a7ad-50153bf6d950" xlink:to="loc_us-gaap_StatementTable_019dac15-a246-7c71-b3e2-c3fb8ba7f9b3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a246-7afe-9a99-c5b5bf1ff010" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-7c71-b3e2-c3fb8ba7f9b3" xlink:to="loc_dei_LegalEntityAxis_019dac15-a246-7afe-9a99-c5b5bf1ff010" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-7afe-9a99-c5b5bf1ff010_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-7afe-9a99-c5b5bf1ff010" xlink:to="loc_dei_EntityDomain_019dac15-a246-7afe-9a99-c5b5bf1ff010_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-78ff-ba47-0be2c450cadb" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-7afe-9a99-c5b5bf1ff010" xlink:to="loc_dei_EntityDomain_019dac15-a246-78ff-ba47-0be2c450cadb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsMember_019dac15-a246-7428-9f5f-db593704d6f2" xlink:href="optu-20260331.xsd#optu_CSCHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a246-78ff-ba47-0be2c450cadb" xlink:to="loc_optu_CSCHoldingsMember_019dac15-a246-7428-9f5f-db593704d6f2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-741e-badc-5602097424cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-7c71-b3e2-c3fb8ba7f9b3" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-741e-badc-5602097424cb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a246-741e-badc-5602097424cb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-741e-badc-5602097424cb" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a246-741e-badc-5602097424cb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a246-7bab-9b72-14e34f2dd21c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-741e-badc-5602097424cb" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a246-7bab-9b72-14e34f2dd21c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dac15-a246-7b1f-b516-593494c6368d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019dac15-a246-7bab-9b72-14e34f2dd21c" xlink:to="loc_us-gaap_RelatedPartyMember_019dac15-a246-7b1f-b516-593494c6368d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019dac15-a246-75a9-9d35-acc5e2183582" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7d22-a7ad-50153bf6d950" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019dac15-a246-75a9-9d35-acc5e2183582" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019dac15-a246-7f3d-a82f-6411922f90d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7d22-a7ad-50153bf6d950" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019dac15-a246-7f3d-a82f-6411922f90d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019dac15-a246-7eb9-99e4-6e3ba638d57f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7d22-a7ad-50153bf6d950" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019dac15-a246-7eb9-99e4-6e3ba638d57f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019dac15-a246-728c-92f3-4f6ada70e59c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7d22-a7ad-50153bf6d950" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019dac15-a246-728c-92f3-4f6ada70e59c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesCurrent_019dac15-a246-744e-906e-1d1f27e18a72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7d22-a7ad-50153bf6d950" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesCurrent_019dac15-a246-744e-906e-1d1f27e18a72" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonUnitIssued_019dac15-a246-720c-9a7e-3d9552894341" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonUnitIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7d22-a7ad-50153bf6d950" xlink:to="loc_us-gaap_CommonUnitIssued_019dac15-a246-720c-9a7e-3d9552894341" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonUnitOutstanding_019dac15-a246-71a1-a34b-b82a7a16098a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonUnitOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7d22-a7ad-50153bf6d950" xlink:to="loc_us-gaap_CommonUnitOutstanding_019dac15-a246-71a1-a34b-b82a7a16098a" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/CSCHOLDINGSCONSOLIDATEDSTATEMENTOFOPERATIONS" xlink:type="simple" xlink:href="optu-20260331.xsd#CSCHOLDINGSCONSOLIDATEDSTATEMENTOFOPERATIONS"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/CSCHOLDINGSCONSOLIDATEDSTATEMENTOFOPERATIONS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dac15-a246-7a11-8967-7db74ac7a6e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dac15-a246-708e-8539-3ad7e7f07ac9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7a11-8967-7db74ac7a6e0" xlink:to="loc_us-gaap_StatementTable_019dac15-a246-708e-8539-3ad7e7f07ac9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a246-732f-8262-031e68cbc542" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-708e-8539-3ad7e7f07ac9" xlink:to="loc_dei_LegalEntityAxis_019dac15-a246-732f-8262-031e68cbc542" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-732f-8262-031e68cbc542_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-732f-8262-031e68cbc542" xlink:to="loc_dei_EntityDomain_019dac15-a246-732f-8262-031e68cbc542_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-70b2-9743-2b305e3bbc95" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-732f-8262-031e68cbc542" xlink:to="loc_dei_EntityDomain_019dac15-a246-70b2-9743-2b305e3bbc95" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsMember_019dac15-a246-77fc-baff-08f664bd8dc8" xlink:href="optu-20260331.xsd#optu_CSCHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a246-70b2-9743-2b305e3bbc95" xlink:to="loc_optu_CSCHoldingsMember_019dac15-a246-77fc-baff-08f664bd8dc8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019dac15-a246-79d5-b16e-3d7526abbebd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7a11-8967-7db74ac7a6e0" xlink:to="loc_us-gaap_Revenues_019dac15-a246-79d5-b16e-3d7526abbebd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpensesAbstract_019dac15-a246-723c-ac70-6a2ee2bf1e27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7a11-8967-7db74ac7a6e0" xlink:to="loc_us-gaap_CostsAndExpensesAbstract_019dac15-a246-723c-ac70-6a2ee2bf1e27" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_019dac15-a246-7379-9d19-92ccf80079cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019dac15-a246-723c-ac70-6a2ee2bf1e27" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_019dac15-a246-7379-9d19-92ccf80079cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCostAndExpenseOperating_019dac15-a246-7638-9f4f-f097f5529917" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCostAndExpenseOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019dac15-a246-723c-ac70-6a2ee2bf1e27" xlink:to="loc_us-gaap_OtherCostAndExpenseOperating_019dac15-a246-7638-9f4f-f097f5529917" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_RestructuringandOtherExpense_019dac15-a246-7404-a39a-34641b55dd51" xlink:href="optu-20260331.xsd#optu_RestructuringandOtherExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019dac15-a246-723c-ac70-6a2ee2bf1e27" xlink:to="loc_optu_RestructuringandOtherExpense_019dac15-a246-7404-a39a-34641b55dd51" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019dac15-a246-7628-85e6-432a590bfb74" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019dac15-a246-723c-ac70-6a2ee2bf1e27" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019dac15-a246-7628-85e6-432a590bfb74" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_019dac15-a246-739d-8326-226474817ded" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019dac15-a246-723c-ac70-6a2ee2bf1e27" xlink:to="loc_us-gaap_CostsAndExpenses_019dac15-a246-739d-8326-226474817ded" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019dac15-a246-7bac-a03f-b62a3ad15a69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7a11-8967-7db74ac7a6e0" xlink:to="loc_us-gaap_OperatingIncomeLoss_019dac15-a246-7bac-a03f-b62a3ad15a69" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019dac15-a246-7469-8cd5-4c8f1816c21d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7a11-8967-7db74ac7a6e0" xlink:to="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019dac15-a246-7469-8cd5-4c8f1816c21d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNet_019dac15-a246-7cb7-9cd1-a5380589ebb7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeExpenseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019dac15-a246-7469-8cd5-4c8f1816c21d" xlink:to="loc_us-gaap_InterestIncomeExpenseNet_019dac15-a246-7cb7-9cd1-a5380589ebb7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnInvestments_019dac15-a246-754a-b69b-13ad1a4612d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019dac15-a246-7469-8cd5-4c8f1816c21d" xlink:to="loc_us-gaap_GainLossOnInvestments_019dac15-a246-754a-b69b-13ad1a4612d7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnInterestRateDerivativeInstrumentsNotDesignatedAsHedgingInstruments_019dac15-a246-7b2d-9536-59a116e0f04f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnInterestRateDerivativeInstrumentsNotDesignatedAsHedgingInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019dac15-a246-7469-8cd5-4c8f1816c21d" xlink:to="loc_us-gaap_GainLossOnInterestRateDerivativeInstrumentsNotDesignatedAsHedgingInstruments_019dac15-a246-7b2d-9536-59a116e0f04f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019dac15-a246-7653-bca3-a3dddcca4929" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019dac15-a246-7469-8cd5-4c8f1816c21d" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019dac15-a246-7653-bca3-a3dddcca4929" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019dac15-a246-7f62-a01d-dbbe4d6665b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019dac15-a246-7469-8cd5-4c8f1816c21d" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019dac15-a246-7f62-a01d-dbbe4d6665b6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_019dac15-a246-791d-8a4b-86af0229c32f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019dac15-a246-7469-8cd5-4c8f1816c21d" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_019dac15-a246-791d-8a4b-86af0229c32f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019dac15-a246-7d53-b26e-8523b69cad27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7a11-8967-7db74ac7a6e0" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019dac15-a246-7d53-b26e-8523b69cad27" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019dac15-a246-781c-96f3-bb34da3fe778" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7a11-8967-7db74ac7a6e0" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019dac15-a246-781c-96f3-bb34da3fe778" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019dac15-a246-7ea5-bee0-2f7727e7f64e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7a11-8967-7db74ac7a6e0" xlink:to="loc_us-gaap_ProfitLoss_019dac15-a246-7ea5-bee0-2f7727e7f64e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_019dac15-a246-7d33-a5ee-d23d6bc980ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7a11-8967-7db74ac7a6e0" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_019dac15-a246-7d33-a5ee-d23d6bc980ee" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019dac15-a246-76d7-b039-1b75c4a03784" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7a11-8967-7db74ac7a6e0" xlink:to="loc_us-gaap_NetIncomeLoss_019dac15-a246-76d7-b039-1b75c4a03784" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/CSCHOLDINGSCONSOLIDATEDSTATEMENTOFOPERATIONSParenthetical" xlink:type="simple" xlink:href="optu-20260331.xsd#CSCHOLDINGSCONSOLIDATEDSTATEMENTOFOPERATIONSParenthetical"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/CSCHOLDINGSCONSOLIDATEDSTATEMENTOFOPERATIONSParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dac15-a246-74cf-b57a-52a4e21f2a80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dac15-a246-7610-a6fc-508416ba9e2c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-74cf-b57a-52a4e21f2a80" xlink:to="loc_us-gaap_StatementTable_019dac15-a246-7610-a6fc-508416ba9e2c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a246-782d-8937-1501da9302e7" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-7610-a6fc-508416ba9e2c" xlink:to="loc_dei_LegalEntityAxis_019dac15-a246-782d-8937-1501da9302e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-782d-8937-1501da9302e7_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-782d-8937-1501da9302e7" xlink:to="loc_dei_EntityDomain_019dac15-a246-782d-8937-1501da9302e7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-77d8-9d67-02e384854234" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-782d-8937-1501da9302e7" xlink:to="loc_dei_EntityDomain_019dac15-a246-77d8-9d67-02e384854234" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsMember_019dac15-a246-76f0-902b-782239db2022" xlink:href="optu-20260331.xsd#optu_CSCHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a246-77d8-9d67-02e384854234" xlink:to="loc_optu_CSCHoldingsMember_019dac15-a246-76f0-902b-782239db2022" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-7cf7-bd66-4c3183582872" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-7610-a6fc-508416ba9e2c" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-7cf7-bd66-4c3183582872" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a246-7cf7-bd66-4c3183582872_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-7cf7-bd66-4c3183582872" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a246-7cf7-bd66-4c3183582872_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a246-7de0-9706-484dde6a72c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a246-7cf7-bd66-4c3183582872" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a246-7de0-9706-484dde6a72c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dac15-a246-7dc6-b58c-e0115729a9bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019dac15-a246-7de0-9706-484dde6a72c9" xlink:to="loc_us-gaap_RelatedPartyMember_019dac15-a246-7dc6-b58c-e0115729a9bb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019dac15-a246-7cb7-8575-4850d5655d51" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-74cf-b57a-52a4e21f2a80" xlink:to="loc_us-gaap_Revenues_019dac15-a246-7cb7-8575-4850d5655d51" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_019dac15-a246-72fe-8372-685bc93bc9f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-74cf-b57a-52a4e21f2a80" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_019dac15-a246-72fe-8372-685bc93bc9f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCostAndExpenseOperating_019dac15-a246-795f-8c37-a14e2629d538" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCostAndExpenseOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-74cf-b57a-52a4e21f2a80" xlink:to="loc_us-gaap_OtherCostAndExpenseOperating_019dac15-a246-795f-8c37-a14e2629d538" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/CSCHOLDINGSCONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMELOSS" xlink:type="simple" xlink:href="optu-20260331.xsd#CSCHOLDINGSCONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMELOSS"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/CSCHOLDINGSCONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMELOSS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dac15-a246-7c0e-aad8-3e6d85c2ee79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dac15-a246-7e9e-b71b-0dfb4be40405" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7c0e-aad8-3e6d85c2ee79" xlink:to="loc_us-gaap_StatementTable_019dac15-a246-7e9e-b71b-0dfb4be40405" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a246-72c0-b9ef-2e28c06080aa" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-7e9e-b71b-0dfb4be40405" xlink:to="loc_dei_LegalEntityAxis_019dac15-a246-72c0-b9ef-2e28c06080aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-72c0-b9ef-2e28c06080aa_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-72c0-b9ef-2e28c06080aa" xlink:to="loc_dei_EntityDomain_019dac15-a246-72c0-b9ef-2e28c06080aa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-7b5b-b308-c0794ae31b1a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-72c0-b9ef-2e28c06080aa" xlink:to="loc_dei_EntityDomain_019dac15-a246-7b5b-b308-c0794ae31b1a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsMember_019dac15-a246-7417-8306-9049ab31f04f" xlink:href="optu-20260331.xsd#optu_CSCHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a246-7b5b-b308-c0794ae31b1a" xlink:to="loc_optu_CSCHoldingsMember_019dac15-a246-7417-8306-9049ab31f04f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019dac15-a246-7fec-889d-5fa73851eb51" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7c0e-aad8-3e6d85c2ee79" xlink:to="loc_us-gaap_ProfitLoss_019dac15-a246-7fec-889d-5fa73851eb51" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_019dac15-a246-7878-b12f-68a3c300672c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7c0e-aad8-3e6d85c2ee79" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_019dac15-a246-7878-b12f-68a3c300672c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_019dac15-a246-7c18-a7ca-69a34185eba0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_019dac15-a246-7878-b12f-68a3c300672c" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_019dac15-a246-7c18-a7ca-69a34185eba0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax_019dac15-a246-7f19-bba2-d50fffd111ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_019dac15-a246-7c18-a7ca-69a34185eba0" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax_019dac15-a246-7f19-bba2-d50fffd111ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax_019dac15-a246-7464-bbfe-0b288d78bf8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_019dac15-a246-7c18-a7ca-69a34185eba0" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax_019dac15-a246-7464-bbfe-0b288d78bf8b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax_019dac15-a246-7bc3-921e-cff42d84dadc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_019dac15-a246-7c18-a7ca-69a34185eba0" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax_019dac15-a246-7bc3-921e-cff42d84dadc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax_019dac15-a246-7efe-8301-8b66e0568799" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_019dac15-a246-7c18-a7ca-69a34185eba0" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax_019dac15-a246-7efe-8301-8b66e0568799" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019dac15-a246-7663-a277-8ef25881cab9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_019dac15-a246-7878-b12f-68a3c300672c" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019dac15-a246-7663-a277-8ef25881cab9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_019dac15-a246-788f-be54-71a7dfdcfa43" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7c0e-aad8-3e6d85c2ee79" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_019dac15-a246-788f-be54-71a7dfdcfa43" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_019dac15-a246-7354-a47e-b554377f9526" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7c0e-aad8-3e6d85c2ee79" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_019dac15-a246-7354-a47e-b554377f9526" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_019dac15-a246-7286-99e7-37827ca1d795" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-7c0e-aad8-3e6d85c2ee79" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_019dac15-a246-7286-99e7-37827ca1d795" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/CSCHOLDINGSCONSOLIDATEDSTATEMENTOFMEMBERSEQUITY" xlink:type="simple" xlink:href="optu-20260331.xsd#CSCHOLDINGSCONSOLIDATEDSTATEMENTOFMEMBERSEQUITY"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/CSCHOLDINGSCONSOLIDATEDSTATEMENTOFMEMBERSEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dac15-a246-76d7-9879-d21e37a8ff44" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dac15-a246-70e4-9253-5a41efac6b0a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-76d7-9879-d21e37a8ff44" xlink:to="loc_us-gaap_StatementTable_019dac15-a246-70e4-9253-5a41efac6b0a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a246-75ef-a1a5-0e3363361406" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-70e4-9253-5a41efac6b0a" xlink:to="loc_dei_LegalEntityAxis_019dac15-a246-75ef-a1a5-0e3363361406" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-75ef-a1a5-0e3363361406_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-75ef-a1a5-0e3363361406" xlink:to="loc_dei_EntityDomain_019dac15-a246-75ef-a1a5-0e3363361406_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-7c40-a922-117c212a5490" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-75ef-a1a5-0e3363361406" xlink:to="loc_dei_EntityDomain_019dac15-a246-7c40-a922-117c212a5490" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsMember_019dac15-a246-7eb2-bbf2-cae3e64cd92d" xlink:href="optu-20260331.xsd#optu_CSCHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a246-7c40-a922-117c212a5490" xlink:to="loc_optu_CSCHoldingsMember_019dac15-a246-7eb2-bbf2-cae3e64cd92d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019dac15-a246-7c16-9b7c-9392aa0a8122" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-70e4-9253-5a41efac6b0a" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019dac15-a246-7c16-9b7c-9392aa0a8122" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dac15-a246-7c16-9b7c-9392aa0a8122_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dac15-a246-7c16-9b7c-9392aa0a8122" xlink:to="loc_us-gaap_EquityComponentDomain_019dac15-a246-7c16-9b7c-9392aa0a8122_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dac15-a246-780a-beb2-99fbe4dd26f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dac15-a246-7c16-9b7c-9392aa0a8122" xlink:to="loc_us-gaap_EquityComponentDomain_019dac15-a246-780a-beb2-99fbe4dd26f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParentMember_019dac15-a246-77d4-8017-adcc5fe4bd54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dac15-a246-780a-beb2-99fbe4dd26f4" xlink:to="loc_us-gaap_ParentMember_019dac15-a246-77d4-8017-adcc5fe4bd54" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019dac15-a246-7f83-a64f-86f8a5286ef0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019dac15-a246-77d4-8017-adcc5fe4bd54" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019dac15-a246-7f83-a64f-86f8a5286ef0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dac15-a246-7959-9496-a4cff9bf6167" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019dac15-a246-77d4-8017-adcc5fe4bd54" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dac15-a246-7959-9496-a4cff9bf6167" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_019dac15-a246-7a3d-8d51-b3b4adedc5c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dac15-a246-780a-beb2-99fbe4dd26f4" xlink:to="loc_us-gaap_NoncontrollingInterestMember_019dac15-a246-7a3d-8d51-b3b4adedc5c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-793c-947b-55453c38726f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-76d7-9879-d21e37a8ff44" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-793c-947b-55453c38726f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_019dac15-a246-78a8-8b94-e9158c45a69f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-793c-947b-55453c38726f" xlink:to="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_019dac15-a246-78a8-8b94-e9158c45a69f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019dac15-a246-7eb7-917d-4e71aef1c68f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-793c-947b-55453c38726f" xlink:to="loc_us-gaap_NetIncomeLoss_019dac15-a246-7eb7-917d-4e71aef1c68f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_019dac15-a246-7b7c-8475-d649e30c6390" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-793c-947b-55453c38726f" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_019dac15-a246-7b7c-8475-d649e30c6390" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_019dac15-a246-7caf-b4cd-bad56112aeb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-793c-947b-55453c38726f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_019dac15-a246-7caf-b4cd-bad56112aeb3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_019dac15-a246-702f-999c-c4c874b99c27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-793c-947b-55453c38726f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_019dac15-a246-702f-999c-c4c874b99c27" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019dac15-a246-704f-98ad-87fd07a0cd5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-793c-947b-55453c38726f" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019dac15-a246-704f-98ad-87fd07a0cd5e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityOther_019dac15-a246-7e21-832f-91c42b3d7d37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-793c-947b-55453c38726f" xlink:to="loc_us-gaap_StockholdersEquityOther_019dac15-a246-7e21-832f-91c42b3d7d37" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_NonCashContributionsFromParent_019dac15-a246-71d4-badb-b55298056272" xlink:href="optu-20260331.xsd#optu_NonCashContributionsFromParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-793c-947b-55453c38726f" xlink:to="loc_optu_NonCashContributionsFromParent_019dac15-a246-71d4-badb-b55298056272" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_Membershipequitybeforenoncontrollinginterest_019dac15-a246-7bae-9f7c-d0f06e287242" xlink:href="optu-20260331.xsd#optu_Membershipequitybeforenoncontrollinginterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-793c-947b-55453c38726f" xlink:to="loc_optu_Membershipequitybeforenoncontrollinginterest_019dac15-a246-7bae-9f7c-d0f06e287242" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dac15-a246-7fd1-a6f4-3b562dd8913b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-793c-947b-55453c38726f" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dac15-a246-7fd1-a6f4-3b562dd8913b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_Membershipinterestbeforeaccumulatedcomprehensiveloss_019dac15-a246-7e91-a5d3-33d12cda5f54" xlink:href="optu-20260331.xsd#optu_Membershipinterestbeforeaccumulatedcomprehensiveloss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-793c-947b-55453c38726f" xlink:to="loc_optu_Membershipinterestbeforeaccumulatedcomprehensiveloss_019dac15-a246-7e91-a5d3-33d12cda5f54" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterest_019dac15-a246-7605-aca4-51bdcb9ca20a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019dac15-a246-793c-947b-55453c38726f" xlink:to="loc_us-gaap_MinorityInterest_019dac15-a246-7605-aca4-51bdcb9ca20a" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_019dac15-a246-7af9-b23e-4ba33876b0eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_019dac15-a246-7cfb-8762-d0e8a459e6bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-76d7-9879-d21e37a8ff44" xlink:to="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_019dac15-a246-7cfb-8762-d0e8a459e6bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_DistributionMadeToAnEntityUnderCommonControl_019de3a9-9f25-7f6f-ad55-f83077aeebdf" xlink:href="optu-20260331.xsd#optu_DistributionMadeToAnEntityUnderCommonControl"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-76d7-9879-d21e37a8ff44" xlink:to="loc_optu_DistributionMadeToAnEntityUnderCommonControl_019de3a9-9f25-7f6f-ad55-f83077aeebdf" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/CSCHOLDINGSCONSOLIDATEDSTATEMENTOFCASHFLOWS" xlink:type="simple" xlink:href="optu-20260331.xsd#CSCHOLDINGSCONSOLIDATEDSTATEMENTOFCASHFLOWS"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/CSCHOLDINGSCONSOLIDATEDSTATEMENTOFCASHFLOWS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dac15-a246-75e8-9c98-b090caf6d37d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dac15-a246-7f27-aee7-27eb2aa1c43e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-75e8-9c98-b090caf6d37d" xlink:to="loc_us-gaap_StatementTable_019dac15-a246-7f27-aee7-27eb2aa1c43e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a246-74b9-a5d9-3d212d96bbcb" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dac15-a246-7f27-aee7-27eb2aa1c43e" xlink:to="loc_dei_LegalEntityAxis_019dac15-a246-74b9-a5d9-3d212d96bbcb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-74b9-a5d9-3d212d96bbcb_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-74b9-a5d9-3d212d96bbcb" xlink:to="loc_dei_EntityDomain_019dac15-a246-74b9-a5d9-3d212d96bbcb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a246-7ba3-bece-256d4cb1e58c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a246-74b9-a5d9-3d212d96bbcb" xlink:to="loc_dei_EntityDomain_019dac15-a246-7ba3-bece-256d4cb1e58c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsMember_019dac15-a246-7744-8730-79cdf50b8861" xlink:href="optu-20260331.xsd#optu_CSCHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a246-7ba3-bece-256d4cb1e58c" xlink:to="loc_optu_CSCHoldingsMember_019dac15-a246-7744-8730-79cdf50b8861" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-78bc-9e61-9f8de6b0c7de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-75e8-9c98-b090caf6d37d" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-78bc-9e61-9f8de6b0c7de" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019dac15-a246-72ef-b87e-5963dd5e68d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-78bc-9e61-9f8de6b0c7de" xlink:to="loc_us-gaap_ProfitLoss_019dac15-a246-72ef-b87e-5963dd5e68d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-7b3f-a79d-5a5af7a94c57" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-78bc-9e61-9f8de6b0c7de" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-7b3f-a79d-5a5af7a94c57" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019dac15-a246-7a7e-b70c-d939201ef37f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-7b3f-a79d-5a5af7a94c57" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019dac15-a246-7a7e-b70c-d939201ef37f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillAndIntangibleAssetImpairment_019dac15-a246-7973-a386-f771d2b02630" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillAndIntangibleAssetImpairment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-7b3f-a79d-5a5af7a94c57" xlink:to="loc_us-gaap_GoodwillAndIntangibleAssetImpairment_019dac15-a246-7973-a386-f771d2b02630" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_GainLossOnInvestmentsAndSaleOfAffiliateInterestsNet_019dac15-a246-711e-b84c-5928382c5d6e" xlink:href="optu-20260331.xsd#optu_GainLossOnInvestmentsAndSaleOfAffiliateInterestsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-7b3f-a79d-5a5af7a94c57" xlink:to="loc_optu_GainLossOnInvestmentsAndSaleOfAffiliateInterestsNet_019dac15-a246-711e-b84c-5928382c5d6e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019dac15-a246-76b9-8897-231a88144a1c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-7b3f-a79d-5a5af7a94c57" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019dac15-a246-76b9-8897-231a88144a1c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_019dac15-a246-7fd0-9d9a-d94d63eac9be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfFinancingCostsAndDiscounts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-7b3f-a79d-5a5af7a94c57" xlink:to="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_019dac15-a246-7fd0-9d9a-d94d63eac9be" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_019dac15-a246-7d86-9a6c-795282672c78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-7b3f-a79d-5a5af7a94c57" xlink:to="loc_us-gaap_ShareBasedCompensation_019dac15-a246-7d86-9a6c-795282672c78" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_019dac15-a246-7c8a-82ce-afec1c39891f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-7b3f-a79d-5a5af7a94c57" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_019dac15-a246-7c8a-82ce-afec1c39891f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense_019dac15-a246-789a-afc6-f172406e87e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-7b3f-a79d-5a5af7a94c57" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense_019dac15-a246-789a-afc6-f172406e87e6" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProvisionForDoubtfulAccounts_019dac15-a246-7580-83ce-aa3e3680b041" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProvisionForDoubtfulAccounts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-7b3f-a79d-5a5af7a94c57" xlink:to="loc_us-gaap_ProvisionForDoubtfulAccounts_019dac15-a246-7580-83ce-aa3e3680b041" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherOperatingActivitiesCashFlowStatement_019dac15-a246-799c-975e-cbe9321c025c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherOperatingActivitiesCashFlowStatement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-7b3f-a79d-5a5af7a94c57" xlink:to="loc_us-gaap_OtherOperatingActivitiesCashFlowStatement_019dac15-a246-799c-975e-cbe9321c025c" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dac15-a246-7061-9165-70526eab6e82" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-7b3f-a79d-5a5af7a94c57" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dac15-a246-7061-9165-70526eab6e82" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_019dac15-a246-74ac-9e5c-c23d81797775" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dac15-a246-7061-9165-70526eab6e82" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_019dac15-a246-74ac-9e5c-c23d81797775" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_019dac15-a246-7999-8bd3-063785588fc5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dac15-a246-7061-9165-70526eab6e82" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_019dac15-a246-7999-8bd3-063785588fc5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseDueFromAffiliates_019dac15-a246-76ec-9af1-a652561d7b81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseDueFromAffiliates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dac15-a246-7061-9165-70526eab6e82" xlink:to="loc_us-gaap_IncreaseDecreaseDueFromAffiliates_019dac15-a246-76ec-9af1-a652561d7b81" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_019dac15-a246-75a6-8233-71fcffb6c4f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dac15-a246-7061-9165-70526eab6e82" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_019dac15-a246-75a6-8233-71fcffb6c4f2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInInterestPayableNet_019dac15-a246-758b-b26c-fd0144846ce0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInInterestPayableNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dac15-a246-7061-9165-70526eab6e82" xlink:to="loc_us-gaap_IncreaseDecreaseInInterestPayableNet_019dac15-a246-758b-b26c-fd0144846ce0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInDeferredRevenue_019dac15-a246-7a33-84ce-726bc472f81a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInDeferredRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dac15-a246-7061-9165-70526eab6e82" xlink:to="loc_us-gaap_IncreaseDecreaseInDeferredRevenue_019dac15-a246-7a33-84ce-726bc472f81a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInDerivativeLiabilities_019dac15-a246-7c83-aca6-6f0fbb4f810e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInDerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dac15-a246-7061-9165-70526eab6e82" xlink:to="loc_us-gaap_IncreaseDecreaseInDerivativeLiabilities_019dac15-a246-7c83-aca6-6f0fbb4f810e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019dac15-a246-719f-9633-7f5c0213da46" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019dac15-a246-78bc-9e61-9f8de6b0c7de" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019dac15-a246-719f-9633-7f5c0213da46" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dac15-a246-7b74-8c27-b0424420a8a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-75e8-9c98-b090caf6d37d" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dac15-a246-7b74-8c27-b0424420a8a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_019dac15-a246-7468-94e5-7dd966ed19c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dac15-a246-7b74-8c27-b0424420a8a1" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_019dac15-a246-7468-94e5-7dd966ed19c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_019dac15-a246-7638-81d0-6ec0cfbd7f47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dac15-a246-7b74-8c27-b0424420a8a1" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_019dac15-a246-7638-81d0-6ec0cfbd7f47" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_019dac15-a246-7b93-b743-9619696f11c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dac15-a246-7b74-8c27-b0424420a8a1" xlink:to="loc_us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_019dac15-a246-7b93-b743-9619696f11c1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireIntangibleAssets_019dac15-a246-706e-9277-9b813baaa012" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dac15-a246-7b74-8c27-b0424420a8a1" xlink:to="loc_us-gaap_PaymentsToAcquireIntangibleAssets_019dac15-a246-706e-9277-9b813baaa012" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_019dac15-a246-7f99-a2a5-35f38d4f62d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForProceedsFromOtherInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dac15-a246-7b74-8c27-b0424420a8a1" xlink:to="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_019dac15-a246-7f99-a2a5-35f38d4f62d3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019dac15-a246-73d9-a12a-9cc05b2e5163" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dac15-a246-7b74-8c27-b0424420a8a1" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019dac15-a246-73d9-a12a-9cc05b2e5163" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dac15-a246-749a-ba85-345dd5ecfb37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-75e8-9c98-b090caf6d37d" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dac15-a246-749a-ba85-345dd5ecfb37" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_019dac15-a246-7da5-bb7d-299cb42671e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dac15-a246-749a-ba85-345dd5ecfb37" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_019dac15-a246-7da5-bb7d-299cb42671e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_019dac15-a246-7790-b8df-833bf6600c08" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dac15-a246-749a-ba85-345dd5ecfb37" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_019dac15-a246-7790-b8df-833bf6600c08" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromRelatedPartyDebt_019dac15-a246-766e-bae3-d2084b1cff32" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromRelatedPartyDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dac15-a246-749a-ba85-345dd5ecfb37" xlink:to="loc_us-gaap_ProceedsFromRelatedPartyDebt_019dac15-a246-766e-bae3-d2084b1cff32" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividends_019dac15-a246-72b4-8b54-9074a37d4268" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfDividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dac15-a246-749a-ba85-345dd5ecfb37" xlink:to="loc_us-gaap_PaymentsOfDividends_019dac15-a246-72b4-8b54-9074a37d4268" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeasePrincipalPayments_019dac15-a246-723a-a7f5-b8a1e7693200" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinanceLeasePrincipalPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dac15-a246-749a-ba85-345dd5ecfb37" xlink:to="loc_us-gaap_FinanceLeasePrincipalPayments_019dac15-a246-723a-a7f5-b8a1e7693200" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_PaymentToAcquireNoncontrollingInterest_019dac15-a246-78cf-b77f-38374e96e253" xlink:href="optu-20260331.xsd#optu_PaymentToAcquireNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dac15-a246-749a-ba85-345dd5ecfb37" xlink:to="loc_optu_PaymentToAcquireNoncontrollingInterest_019dac15-a246-78cf-b77f-38374e96e253" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfFinancingCosts_019dac15-a246-7140-a501-61fe01aae78e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dac15-a246-749a-ba85-345dd5ecfb37" xlink:to="loc_us-gaap_PaymentsOfFinancingCosts_019dac15-a246-7140-a501-61fe01aae78e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_019dac15-a246-7c23-b920-fd84944f735e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromPaymentsForOtherFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dac15-a246-749a-ba85-345dd5ecfb37" xlink:to="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_019dac15-a246-7c23-b920-fd84944f735e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromPaymentsToMinorityShareholders_019dac15-a246-7939-ba75-7e31392ab7be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromPaymentsToMinorityShareholders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dac15-a246-749a-ba85-345dd5ecfb37" xlink:to="loc_us-gaap_ProceedsFromPaymentsToMinorityShareholders_019dac15-a246-7939-ba75-7e31392ab7be" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019dac15-a246-7365-bbe3-9e39eaee3d1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dac15-a246-749a-ba85-345dd5ecfb37" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019dac15-a246-7365-bbe3-9e39eaee3d1f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect_019dac15-a246-7e66-8ed3-d57465418c48" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-75e8-9c98-b090caf6d37d" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect_019dac15-a246-7e66-8ed3-d57465418c48" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019dac15-a246-76e6-a27d-a7606cb664fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-75e8-9c98-b090caf6d37d" xlink:to="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019dac15-a246-76e6-a27d-a7606cb664fa" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019dac15-a246-711f-8223-d8ba1600f64d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-75e8-9c98-b090caf6d37d" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019dac15-a246-711f-8223-d8ba1600f64d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019dac15-a246-71eb-8543-9ceeb85589f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dac15-a246-75e8-9c98-b090caf6d37d" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019dac15-a246-71eb-8543-9ceeb85589f2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019dac15-a246-771c-a090-51659e664d49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/RevenueRecognitionandDeferredRevenueDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#RevenueRecognitionandDeferredRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/RevenueRecognitionandDeferredRevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019dac15-a333-7b1e-b0f1-59b2b47d3e71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019dac15-a333-7086-a4d1-2bba5a1a83df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019dac15-a333-7b1e-b0f1-59b2b47d3e71" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019dac15-a333-7086-a4d1-2bba5a1a83df" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019dac15-a333-7612-8e17-ea6406d41e02" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019dac15-a333-7086-a4d1-2bba5a1a83df" xlink:to="loc_srt_ProductOrServiceAxis_019dac15-a333-7612-8e17-ea6406d41e02" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019dac15-a333-7612-8e17-ea6406d41e02_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019dac15-a333-7612-8e17-ea6406d41e02" xlink:to="loc_srt_ProductsAndServicesDomain_019dac15-a333-7612-8e17-ea6406d41e02_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019dac15-a333-70fc-9c06-c635e3913c1c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019dac15-a333-7612-8e17-ea6406d41e02" xlink:to="loc_srt_ProductsAndServicesDomain_019dac15-a333-70fc-9c06-c635e3913c1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_TotalResidentialRevenueMember_019dac15-a333-792e-9d37-9385df85d331" xlink:href="optu-20260331.xsd#optu_TotalResidentialRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019dac15-a333-70fc-9c06-c635e3913c1c" xlink:to="loc_optu_TotalResidentialRevenueMember_019dac15-a333-792e-9d37-9385df85d331" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_BroadbandMember_019dac15-a333-7aba-ba1e-3f068015e659" xlink:href="optu-20260331.xsd#optu_BroadbandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_optu_TotalResidentialRevenueMember_019dac15-a333-792e-9d37-9385df85d331" xlink:to="loc_optu_BroadbandMember_019dac15-a333-7aba-ba1e-3f068015e659" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_PayTVMember_019dac15-a333-7dce-b47c-ead08c4b2602" xlink:href="optu-20260331.xsd#optu_PayTVMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_optu_TotalResidentialRevenueMember_019dac15-a333-792e-9d37-9385df85d331" xlink:to="loc_optu_PayTVMember_019dac15-a333-7dce-b47c-ead08c4b2602" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_TelephonyMember_019dac15-a333-7007-8842-12cf9465356c" xlink:href="optu-20260331.xsd#optu_TelephonyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_optu_TotalResidentialRevenueMember_019dac15-a333-792e-9d37-9385df85d331" xlink:to="loc_optu_TelephonyMember_019dac15-a333-7007-8842-12cf9465356c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_MobileServicesMember_019dac15-a333-792d-9a32-315e6a04f065" xlink:href="optu-20260331.xsd#optu_MobileServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_optu_TotalResidentialRevenueMember_019dac15-a333-792e-9d37-9385df85d331" xlink:to="loc_optu_MobileServicesMember_019dac15-a333-792d-9a32-315e6a04f065" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_BusinessServicesandWholesaleMember_019dac15-a333-79aa-aa42-5d37c3b3dc9e" xlink:href="optu-20260331.xsd#optu_BusinessServicesandWholesaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019dac15-a333-70fc-9c06-c635e3913c1c" xlink:to="loc_optu_BusinessServicesandWholesaleMember_019dac15-a333-79aa-aa42-5d37c3b3dc9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_AdvertisingandNewsMember_019dac15-a333-765b-8f94-1c6a4893a9cd" xlink:href="optu-20260331.xsd#optu_AdvertisingandNewsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019dac15-a333-70fc-9c06-c635e3913c1c" xlink:to="loc_optu_AdvertisingandNewsMember_019dac15-a333-765b-8f94-1c6a4893a9cd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_ProductsAndServicesOtherIncludingMobileEquipmentMember_019dac15-a333-7301-975e-98d1db5ede93" xlink:href="optu-20260331.xsd#optu_ProductsAndServicesOtherIncludingMobileEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019dac15-a333-70fc-9c06-c635e3913c1c" xlink:to="loc_optu_ProductsAndServicesOtherIncludingMobileEquipmentMember_019dac15-a333-7301-975e-98d1db5ede93" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FranchiseMember_019dac15-a333-7770-987d-da4557c4c5a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FranchiseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019dac15-a333-70fc-9c06-c635e3913c1c" xlink:to="loc_us-gaap_FranchiseMember_019dac15-a333-7770-987d-da4557c4c5a0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019dac15-a333-7de8-828c-9a70a61758c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019dac15-a333-7086-a4d1-2bba5a1a83df" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019dac15-a333-7de8-828c-9a70a61758c5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019dac15-a333-7de8-828c-9a70a61758c5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019dac15-a333-7de8-828c-9a70a61758c5" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019dac15-a333-7de8-828c-9a70a61758c5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019dac15-a333-7355-a4ab-7eb317244721" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019dac15-a333-7de8-828c-9a70a61758c5" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019dac15-a333-7355-a4ab-7eb317244721" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerContractsMember_019dac15-a333-7a27-a89e-3d06ef8cd185" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019dac15-a333-7355-a4ab-7eb317244721" xlink:to="loc_us-gaap_CustomerContractsMember_019dac15-a333-7a27-a89e-3d06ef8cd185" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019dac15-a333-7467-83ff-0f76559963b8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019dac15-a333-7086-a4d1-2bba5a1a83df" xlink:to="loc_srt_RangeAxis_019dac15-a333-7467-83ff-0f76559963b8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019dac15-a333-7467-83ff-0f76559963b8_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019dac15-a333-7467-83ff-0f76559963b8" xlink:to="loc_srt_RangeMember_019dac15-a333-7467-83ff-0f76559963b8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019dac15-a333-7682-a0d2-c1893cb7ec0d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019dac15-a333-7467-83ff-0f76559963b8" xlink:to="loc_srt_RangeMember_019dac15-a333-7682-a0d2-c1893cb7ec0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019dac15-a333-7578-9ccd-87bbea74009d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019dac15-a333-7682-a0d2-c1893cb7ec0d" xlink:to="loc_srt_MinimumMember_019dac15-a333-7578-9ccd-87bbea74009d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019dac15-a333-7ce4-a7c3-5f9cc97b6634" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019dac15-a333-7682-a0d2-c1893cb7ec0d" xlink:to="loc_srt_MaximumMember_019dac15-a333-7ce4-a7c3-5f9cc97b6634" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019dac15-a333-73e0-b457-95eeb69b6dbb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019dac15-a333-7b1e-b0f1-59b2b47d3e71" xlink:to="loc_us-gaap_Revenues_019dac15-a333-73e0-b457-95eeb69b6dbb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_019dac15-a333-78af-abe0-33013a6b236f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019dac15-a333-7b1e-b0f1-59b2b47d3e71" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_019dac15-a333-78af-abe0-33013a6b236f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNet_019dac15-a333-7f6f-90a5-0f8e61c10cd1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019dac15-a333-7b1e-b0f1-59b2b47d3e71" xlink:to="loc_us-gaap_ContractWithCustomerAssetNet_019dac15-a333-7f6f-90a5-0f8e61c10cd1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019dac15-a333-7036-92b8-277649c7dec5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019dac15-a333-7b1e-b0f1-59b2b47d3e71" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019dac15-a333-7036-92b8-277649c7dec5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskCustomer_019dac15-a333-7a59-8223-007a2190b9d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskCustomer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019dac15-a333-7b1e-b0f1-59b2b47d3e71" xlink:to="loc_us-gaap_ConcentrationRiskCustomer_019dac15-a333-7a59-8223-007a2190b9d1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_Concentrationofcustomertotradereceivables_019dac15-a333-7bd7-a2b6-8c16730b433b" xlink:href="optu-20260331.xsd#optu_Concentrationofcustomertotradereceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019dac15-a333-7b1e-b0f1-59b2b47d3e71" xlink:to="loc_optu_Concentrationofcustomertotradereceivables_019dac15-a333-7bd7-a2b6-8c16730b433b" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/SUPPLEMENTALCASHFLOWINFORMATIONReconciliationofCashCashEquivalentsandRestrictedCashDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#SUPPLEMENTALCASHFLOWINFORMATIONReconciliationofCashCashEquivalentsandRestrictedCashDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/SUPPLEMENTALCASHFLOWINFORMATIONReconciliationofCashCashEquivalentsandRestrictedCashDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsLineItems_019dac15-a333-72ac-afec-066fc24fb261" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_019dac15-a333-7d58-8964-575027ece639" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfCashAndCashEquivalentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019dac15-a333-72ac-afec-066fc24fb261" xlink:to="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_019dac15-a333-7d58-8964-575027ece639" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a333-7d62-bb81-0d2867124f37" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_019dac15-a333-7d58-8964-575027ece639" xlink:to="loc_dei_LegalEntityAxis_019dac15-a333-7d62-bb81-0d2867124f37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a333-7d62-bb81-0d2867124f37_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a333-7d62-bb81-0d2867124f37" xlink:to="loc_dei_EntityDomain_019dac15-a333-7d62-bb81-0d2867124f37_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a333-7fef-8598-e5da7eb51a66" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a333-7d62-bb81-0d2867124f37" xlink:to="loc_dei_EntityDomain_019dac15-a333-7fef-8598-e5da7eb51a66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsMember_019dac15-a333-7fd2-be2d-01207de58fa8" xlink:href="optu-20260331.xsd#optu_CSCHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a333-7fef-8598-e5da7eb51a66" xlink:to="loc_optu_CSCHoldingsMember_019dac15-a333-7fd2-be2d-01207de58fa8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019dac15-a333-7e89-b272-2266f9f5f221" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_019dac15-a333-7d58-8964-575027ece639" xlink:to="loc_us-gaap_DebtInstrumentAxis_019dac15-a333-7e89-b272-2266f9f5f221" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a333-7e89-b272-2266f9f5f221_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dac15-a333-7e89-b272-2266f9f5f221" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a333-7e89-b272-2266f9f5f221_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a333-7e18-ac20-51308284ef24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dac15-a333-7e89-b272-2266f9f5f221" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a333-7e18-ac20-51308284ef24" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_ReceivableFacilityLoanMember_019dac15-a333-7bb3-bfd3-7218ec477cc4" xlink:href="optu-20260331.xsd#optu_ReceivableFacilityLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a333-7e18-ac20-51308284ef24" xlink:to="loc_optu_ReceivableFacilityLoanMember_019dac15-a333-7bb3-bfd3-7218ec477cc4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dac15-a333-7658-b256-55dbcf30295f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019dac15-a333-72ac-afec-066fc24fb261" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dac15-a333-7658-b256-55dbcf30295f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashCurrent_019dac15-a333-7556-a4f1-fc7ecc891b91" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019dac15-a333-72ac-afec-066fc24fb261" xlink:to="loc_us-gaap_RestrictedCashCurrent_019dac15-a333-7556-a4f1-fc7ecc891b91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndInvestmentsNoncurrent_019dac15-a333-7be3-9c1f-615e4285e063" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndInvestmentsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019dac15-a333-72ac-afec-066fc24fb261" xlink:to="loc_us-gaap_RestrictedCashAndInvestmentsNoncurrent_019dac15-a333-7be3-9c1f-615e4285e063" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019dac15-a333-7f82-8620-931081d6d82c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019dac15-a333-72ac-afec-066fc24fb261" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019dac15-a333-7f82-8620-931081d6d82c" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/RESTRUCTURINGANDOTHEREXPENSEDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#RESTRUCTURINGANDOTHEREXPENSEDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/RESTRUCTURINGANDOTHEREXPENSEDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_019dac15-a333-7f75-b761-d4a054b11f77" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019dac15-a333-7792-b971-4d014c4dea7d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019dac15-a333-7f75-b761-d4a054b11f77" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019dac15-a333-7792-b971-4d014c4dea7d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_019dac15-a333-7fa7-8015-985872034f80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019dac15-a333-7792-b971-4d014c4dea7d" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_019dac15-a333-7fa7-8015-985872034f80" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019dac15-a333-7fa7-8015-985872034f80_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019dac15-a333-7fa7-8015-985872034f80" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019dac15-a333-7fa7-8015-985872034f80_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019dac15-a333-7c99-b1b9-51d1f7cbb878" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019dac15-a333-7fa7-8015-985872034f80" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019dac15-a333-7c99-b1b9-51d1f7cbb878" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_019dac15-a333-7a0d-8cba-a68cfe61ae11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_019dac15-a333-7c99-b1b9-51d1f7cbb878" xlink:to="loc_us-gaap_EmployeeSeveranceMember_019dac15-a333-7a0d-8cba-a68cfe61ae11" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_FacilityRealignmentandOtherCostsMember_019dac15-a333-7564-b522-529465dfdc7b" xlink:href="optu-20260331.xsd#optu_FacilityRealignmentandOtherCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_019dac15-a333-7c99-b1b9-51d1f7cbb878" xlink:to="loc_optu_FacilityRealignmentandOtherCostsMember_019dac15-a333-7564-b522-529465dfdc7b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_RightOfUseOperatingLeasesMember_019dac15-a333-7b5c-94fa-b31a0d8784de" xlink:href="optu-20260331.xsd#optu_RightOfUseOperatingLeasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_019dac15-a333-7c99-b1b9-51d1f7cbb878" xlink:to="loc_optu_RightOfUseOperatingLeasesMember_019dac15-a333-7b5c-94fa-b31a0d8784de" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_TransactionCostsMember_019dac15-a333-738b-b9fb-b2c648aedc3e" xlink:href="optu-20260331.xsd#optu_TransactionCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_019dac15-a333-7c99-b1b9-51d1f7cbb878" xlink:to="loc_optu_TransactionCostsMember_019dac15-a333-738b-b9fb-b2c648aedc3e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019dac15-a333-7ace-82c0-47bc0c1c4760" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019dac15-a333-7792-b971-4d014c4dea7d" xlink:to="loc_us-gaap_AwardTypeAxis_019dac15-a333-7ace-82c0-47bc0c1c4760" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a333-7ace-82c0-47bc0c1c4760_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019dac15-a333-7ace-82c0-47bc0c1c4760" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a333-7ace-82c0-47bc0c1c4760_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a333-7477-a227-f57da52cd06e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019dac15-a333-7ace-82c0-47bc0c1c4760" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a333-7477-a227-f57da52cd06e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019dac15-a333-74f9-ab3c-4dc1bb5ae856" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a333-7477-a227-f57da52cd06e" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019dac15-a333-74f9-ab3c-4dc1bb5ae856" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongLivedAssetsHeldForSaleByAssetTypeAxis_019dac15-a333-7ed0-bd6f-8b37b3cdfa07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongLivedAssetsHeldForSaleByAssetTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019dac15-a333-7792-b971-4d014c4dea7d" xlink:to="loc_us-gaap_LongLivedAssetsHeldForSaleByAssetTypeAxis_019dac15-a333-7ed0-bd6f-8b37b3cdfa07" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongLivedAssetsHeldForSaleNameDomain_019dac15-a333-7ed0-bd6f-8b37b3cdfa07_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongLivedAssetsHeldForSaleNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongLivedAssetsHeldForSaleByAssetTypeAxis_019dac15-a333-7ed0-bd6f-8b37b3cdfa07" xlink:to="loc_us-gaap_LongLivedAssetsHeldForSaleNameDomain_019dac15-a333-7ed0-bd6f-8b37b3cdfa07_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongLivedAssetsHeldForSaleNameDomain_019dac15-a333-79ab-98a8-3b3144fabb32" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongLivedAssetsHeldForSaleNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongLivedAssetsHeldForSaleByAssetTypeAxis_019dac15-a333-7ed0-bd6f-8b37b3cdfa07" xlink:to="loc_us-gaap_LongLivedAssetsHeldForSaleNameDomain_019dac15-a333-79ab-98a8-3b3144fabb32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_TowerAssetsMember_019dac15-a333-7452-9265-b2db4d3fe9f7" xlink:href="optu-20260331.xsd#optu_TowerAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongLivedAssetsHeldForSaleNameDomain_019dac15-a333-79ab-98a8-3b3144fabb32" xlink:to="loc_optu_TowerAssetsMember_019dac15-a333-7452-9265-b2db4d3fe9f7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossRelatedToLitigationSettlement_019dac15-a333-78f1-b075-1b4f7f31473d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossRelatedToLitigationSettlement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019dac15-a333-7f75-b761-d4a054b11f77" xlink:to="loc_us-gaap_GainLossRelatedToLitigationSettlement_019dac15-a333-78f1-b075-1b4f7f31473d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnDispositionOfAssets_019dac15-a333-729a-8bec-8b6e1923ee31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnDispositionOfAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019dac15-a333-7f75-b761-d4a054b11f77" xlink:to="loc_us-gaap_GainLossOnDispositionOfAssets_019dac15-a333-729a-8bec-8b6e1923ee31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_019dac15-a333-76fb-b48b-890beda282a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019dac15-a333-7f75-b761-d4a054b11f77" xlink:to="loc_us-gaap_RestructuringCharges_019dac15-a333-76fb-b48b-890beda282a5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillAndIntangibleAssetImpairment_019dac15-a333-7e66-bdcf-ec85d704a9a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillAndIntangibleAssetImpairment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019dac15-a333-7f75-b761-d4a054b11f77" xlink:to="loc_us-gaap_GoodwillAndIntangibleAssetImpairment_019dac15-a333-7e66-bdcf-ec85d704a9a4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_019dac15-a333-7850-8299-3403aa961eb1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019dac15-a333-7f75-b761-d4a054b11f77" xlink:to="loc_us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_019dac15-a333-7850-8299-3403aa961eb1" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/INTANGIBLEASSETSSummaryofAcquiredIntangibleAssetsDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#INTANGIBLEASSETSSummaryofAcquiredIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/INTANGIBLEASSETSSummaryofAcquiredIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019dac15-a334-794f-8e5d-e7fe1fdcc07b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_019dac15-a334-7c59-affc-665444c6a9fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019dac15-a334-794f-8e5d-e7fe1fdcc07b" xlink:to="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_019dac15-a334-7c59-affc-665444c6a9fc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019dac15-a334-729e-a7cd-c97a7ca010dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_019dac15-a334-7c59-affc-665444c6a9fc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019dac15-a334-729e-a7cd-c97a7ca010dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019dac15-a334-729e-a7cd-c97a7ca010dc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019dac15-a334-729e-a7cd-c97a7ca010dc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019dac15-a334-729e-a7cd-c97a7ca010dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019dac15-a334-7db6-b74f-46c349312f6d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019dac15-a334-729e-a7cd-c97a7ca010dc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019dac15-a334-7db6-b74f-46c349312f6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_019dac15-a334-7a13-b625-da54e41d204e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019dac15-a334-7db6-b74f-46c349312f6d" xlink:to="loc_us-gaap_CustomerRelationshipsMember_019dac15-a334-7a13-b625-da54e41d204e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_019dac15-a334-7d47-9ded-b4e9fc9f54e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019dac15-a334-7db6-b74f-46c349312f6d" xlink:to="loc_us-gaap_TradeNamesMember_019dac15-a334-7d47-9ded-b4e9fc9f54e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_019dac15-a334-70cc-8621-9a0fef9df44b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019dac15-a334-7db6-b74f-46c349312f6d" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_019dac15-a334-70cc-8621-9a0fef9df44b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019dac15-a334-743a-a4bc-2326a244ce15" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_019dac15-a334-7c59-affc-665444c6a9fc" xlink:to="loc_srt_RangeAxis_019dac15-a334-743a-a4bc-2326a244ce15" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019dac15-a334-743a-a4bc-2326a244ce15_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019dac15-a334-743a-a4bc-2326a244ce15" xlink:to="loc_srt_RangeMember_019dac15-a334-743a-a4bc-2326a244ce15_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019dac15-a334-7149-bb79-7b66d7140695" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019dac15-a334-743a-a4bc-2326a244ce15" xlink:to="loc_srt_RangeMember_019dac15-a334-7149-bb79-7b66d7140695" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019dac15-a334-71e7-a1af-47a8acc83c21" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019dac15-a334-7149-bb79-7b66d7140695" xlink:to="loc_srt_MinimumMember_019dac15-a334-71e7-a1af-47a8acc83c21" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019dac15-a334-7acb-8143-4d2aace5b81d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019dac15-a334-7149-bb79-7b66d7140695" xlink:to="loc_srt_MaximumMember_019dac15-a334-7acb-8143-4d2aace5b81d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019dac15-a334-763a-af09-4c26028e8f18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019dac15-a334-794f-8e5d-e7fe1fdcc07b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019dac15-a334-763a-af09-4c26028e8f18" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019dac15-a334-7a31-8496-e614747684e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019dac15-a334-794f-8e5d-e7fe1fdcc07b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019dac15-a334-7a31-8496-e614747684e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019dac15-a334-7bab-9cd3-70b7f041c106" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019dac15-a334-794f-8e5d-e7fe1fdcc07b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019dac15-a334-7bab-9cd3-70b7f041c106" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019dac15-a334-78e4-a907-502d3678948e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019dac15-a334-794f-8e5d-e7fe1fdcc07b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019dac15-a334-78e4-a907-502d3678948e" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/DEBTOutstandingDebtDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#DEBTOutstandingDebtDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/DEBTOutstandingDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7f64-881b-d06f2ef0f6aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7f64-881b-d06f2ef0f6aa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-72bc-a51f-49ce749fdde4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7f64-881b-d06f2ef0f6aa" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-72bc-a51f-49ce749fdde4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-72bc-a51f-49ce749fdde4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-72bc-a51f-49ce749fdde4" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-72bc-a51f-49ce749fdde4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-739b-961f-a1c23dc6c325" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-72bc-a51f-49ce749fdde4" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-739b-961f-a1c23dc6c325" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_019dac15-a334-7638-960a-2f77fb0ead9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-739b-961f-a1c23dc6c325" xlink:to="loc_us-gaap_SeniorNotesMember_019dac15-a334-7638-960a-2f77fb0ead9f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019dac15-a334-799b-8a16-1193a17ed1c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-739b-961f-a1c23dc6c325" xlink:to="loc_us-gaap_SecuredDebtMember_019dac15-a334-799b-8a16-1193a17ed1c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorSubordinatedNotesMember_019dac15-a334-7d02-96ff-d788e70f72f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorSubordinatedNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-739b-961f-a1c23dc6c325" xlink:to="loc_us-gaap_SeniorSubordinatedNotesMember_019dac15-a334-7d02-96ff-d788e70f72f3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMember_019dac15-a334-779e-b617-b82480b23f93" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-739b-961f-a1c23dc6c325" xlink:to="loc_us-gaap_LongTermDebtMember_019dac15-a334-779e-b617-b82480b23f93" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019dac15-a334-733e-b0a3-24c0a075ae27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7f64-881b-d06f2ef0f6aa" xlink:to="loc_us-gaap_CreditFacilityAxis_019dac15-a334-733e-b0a3-24c0a075ae27" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019dac15-a334-733e-b0a3-24c0a075ae27_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019dac15-a334-733e-b0a3-24c0a075ae27" xlink:to="loc_us-gaap_CreditFacilityDomain_019dac15-a334-733e-b0a3-24c0a075ae27_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019dac15-a334-748c-9f6c-d867f8aebb52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019dac15-a334-733e-b0a3-24c0a075ae27" xlink:to="loc_us-gaap_CreditFacilityDomain_019dac15-a334-748c-9f6c-d867f8aebb52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019dac15-a334-78c5-b750-9ea8c15325c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019dac15-a334-748c-9f6c-d867f8aebb52" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019dac15-a334-78c5-b750-9ea8c15325c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019dac15-a334-7ab6-a12f-cd24f120aa0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019dac15-a334-748c-9f6c-d867f8aebb52" xlink:to="loc_us-gaap_SecuredDebtMember_019dac15-a334-7ab6-a12f-cd24f120aa0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CablevisionLightpathRevolvingCreditFacilityMember_019dac15-a334-7441-8e6e-4883b57196dd" xlink:href="optu-20260331.xsd#optu_CablevisionLightpathRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019dac15-a334-748c-9f6c-d867f8aebb52" xlink:to="loc_optu_CablevisionLightpathRevolvingCreditFacilityMember_019dac15-a334-7441-8e6e-4883b57196dd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorSubordinatedNotesMember_019df46c-5384-750d-93aa-a992adfd1941" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorSubordinatedNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019dac15-a334-748c-9f6c-d867f8aebb52" xlink:to="loc_us-gaap_SeniorSubordinatedNotesMember_019df46c-5384-750d-93aa-a992adfd1941" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-78be-b675-64eb6a4c5093" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7f64-881b-d06f2ef0f6aa" xlink:to="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-78be-b675-64eb6a4c5093" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-78be-b675-64eb6a4c5093_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-78be-b675-64eb6a4c5093" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-78be-b675-64eb6a4c5093_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-78be-b675-64eb6a4c5093" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsCablevision7500NotesDueApril12028Member_019dac15-a334-7152-a4d2-5c688dc608cb" xlink:href="optu-20260331.xsd#optu_CSCHoldingsCablevision7500NotesDueApril12028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_CSCHoldingsCablevision7500NotesDueApril12028Member_019dac15-a334-7152-a4d2-5c688dc608cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldings7.500NotesdueApril12028Member_019dac15-a334-786a-a169-0ebd4925d83c" xlink:href="optu-20260331.xsd#optu_CSCHoldings7.500NotesdueApril12028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_CSCHoldings7.500NotesdueApril12028Member_019dac15-a334-786a-a169-0ebd4925d83c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldings5750NotesDueJanuary152030Member_019dac15-a334-7d4c-8c2f-f99d4aaffce7" xlink:href="optu-20260331.xsd#optu_CSCHoldings5750NotesDueJanuary152030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_CSCHoldings5750NotesDueJanuary152030Member_019dac15-a334-7d4c-8c2f-f99d4aaffce7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldings4625NotesDueDecember12030Member_019dac15-a334-74a2-9a14-368f4ec7a524" xlink:href="optu-20260331.xsd#optu_CSCHoldings4625NotesDueDecember12030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_CSCHoldings4625NotesDueDecember12030Member_019dac15-a334-74a2-9a14-368f4ec7a524" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldings5000NotesDueNovember152031Member_019dac15-a334-7604-9f37-66cf9b408b58" xlink:href="optu-20260331.xsd#optu_CSCHoldings5000NotesDueNovember152031Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_CSCHoldings5000NotesDueNovember152031Member_019dac15-a334-7604-9f37-66cf9b408b58" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldings5.5NotesdueApril152027Member_019dac15-a334-7df3-be30-de26c1d3ae48" xlink:href="optu-20260331.xsd#optu_CSCHoldings5.5NotesdueApril152027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_CSCHoldings5.5NotesdueApril152027Member_019dac15-a334-7df3-be30-de26c1d3ae48" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_A5.375SeniorGuaranteedNotesDueFebruary12028Member_019dac15-a334-7ce5-8331-a79c4fdbb39a" xlink:href="optu-20260331.xsd#optu_A5.375SeniorGuaranteedNotesDueFebruary12028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_A5.375SeniorGuaranteedNotesDueFebruary12028Member_019dac15-a334-7ce5-8331-a79c4fdbb39a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldings6500NotesDueFebruary12029Member_019dac15-a334-7195-a5fb-8b85c3478339" xlink:href="optu-20260331.xsd#optu_CSCHoldings6500NotesDueFebruary12029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_CSCHoldings6500NotesDueFebruary12029Member_019dac15-a334-7195-a5fb-8b85c3478339" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldings4125NotesDueDecember12030Member_019dac15-a334-7646-8aef-062e7e14fd28" xlink:href="optu-20260331.xsd#optu_CSCHoldings4125NotesDueDecember12030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_CSCHoldings4125NotesDueDecember12030Member_019dac15-a334-7646-8aef-062e7e14fd28" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_Cablevision8.0NotesdueApril152020Member_019dac15-a334-74ce-bde6-2c6a0bd33066" xlink:href="optu-20260331.xsd#optu_Cablevision8.0NotesdueApril152020Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_Cablevision8.0NotesdueApril152020Member_019dac15-a334-74ce-bde6-2c6a0bd33066" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldings4500SeniorGuaranteedNotesDueNovember152021Member_019dac15-a334-71ab-9b7a-96747482e701" xlink:href="optu-20260331.xsd#optu_CSCHoldings4500SeniorGuaranteedNotesDueNovember152021Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_CSCHoldings4500SeniorGuaranteedNotesDueNovember152021Member_019dac15-a334-71ab-9b7a-96747482e701" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldings112500SeniorGuaranteedNotesDueMay152028Member_019dac15-a334-7e1f-9c84-62fe621282d0" xlink:href="optu-20260331.xsd#optu_CSCHoldings112500SeniorGuaranteedNotesDueMay152028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_CSCHoldings112500SeniorGuaranteedNotesDueMay152028Member_019dac15-a334-7e1f-9c84-62fe621282d0" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldings11.7500SeniorGuaranteedNotesDueJan312029Member_019dac15-a334-77c9-b536-225f95df0127" xlink:href="optu-20260331.xsd#optu_CSCHoldings11.7500SeniorGuaranteedNotesDueJan312029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_CSCHoldings11.7500SeniorGuaranteedNotesDueJan312029Member_019dac15-a334-77c9-b536-225f95df0127" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsRevolvingCreditFacilityMember_019dac15-a334-7fa2-a596-e03b456cbb1a" xlink:href="optu-20260331.xsd#optu_CSCHoldingsRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_CSCHoldingsRevolvingCreditFacilityMember_019dac15-a334-7fa2-a596-e03b456cbb1a" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_IncrementalTermLoanB5Member_019dac15-a334-7dc9-8e79-019a007703cc" xlink:href="optu-20260331.xsd#optu_IncrementalTermLoanB5Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_IncrementalTermLoanB5Member_019dac15-a334-7dc9-8e79-019a007703cc" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_IncrementalTermLoanB6Member_019dac15-a334-7b71-91e9-5a8d8e76ac89" xlink:href="optu-20260331.xsd#optu_IncrementalTermLoanB6Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_IncrementalTermLoanB6Member_019dac15-a334-7b71-91e9-5a8d8e76ac89" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CablevisionLightpathLLC5625NotesDueSeptember152028Member_019dac15-a334-7dc5-9f43-38a9941d4b90" xlink:href="optu-20260331.xsd#optu_CablevisionLightpathLLC5625NotesDueSeptember152028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_CablevisionLightpathLLC5625NotesDueSeptember152028Member_019dac15-a334-7dc5-9f43-38a9941d4b90" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CablevisionLightpathLLC3875NotesDueSeptember152027Member_019dac15-a334-78f6-a51a-1e4e9d52d7ea" xlink:href="optu-20260331.xsd#optu_CablevisionLightpathLLC3875NotesDueSeptember152027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_CablevisionLightpathLLC3875NotesDueSeptember152027Member_019dac15-a334-78f6-a51a-1e4e9d52d7ea" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CablevisionLightpathTermBLoanMember_019dac15-a334-7877-a926-683e5820ea22" xlink:href="optu-20260331.xsd#optu_CablevisionLightpathTermBLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_CablevisionLightpathTermBLoanMember_019dac15-a334-7877-a926-683e5820ea22" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CablevisionLightpathRevolvingCreditFacilityMember_019dac15-a334-7bfb-b435-ec76c70585b2" xlink:href="optu-20260331.xsd#optu_CablevisionLightpathRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_CablevisionLightpathRevolvingCreditFacilityMember_019dac15-a334-7bfb-b435-ec76c70585b2" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansPayableMember_019dac15-a334-790e-8752-9805a0d20774" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoansPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_us-gaap_LoansPayableMember_019dac15-a334-790e-8752-9805a0d20774" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_ReceivableFacilityLoanMember_019dac15-a334-7bf8-8806-fa00b4b6d548" xlink:href="optu-20260331.xsd#optu_ReceivableFacilityLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_ReceivableFacilityLoanMember_019dac15-a334-7bf8-8806-fa00b4b6d548" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_UnsubGroupCreditFacilityMember_019df46c-5384-72ea-b6bf-e10032bbfd48" xlink:href="optu-20260331.xsd#optu_UnsubGroupCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_UnsubGroupCreditFacilityMember_019df46c-5384-72ea-b6bf-e10032bbfd48" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_NYCABSReceivableFacilityLoanMember_019df46c-877a-76e0-834b-5dabfb6db199" xlink:href="optu-20260331.xsd#optu_NYCABSReceivableFacilityLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73cd-89cc-2c840d315d2c" xlink:to="loc_optu_NYCABSReceivableFacilityLoanMember_019df46c-877a-76e0-834b-5dabfb6db199" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a334-7cd4-a6a7-bc375009f839" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7f64-881b-d06f2ef0f6aa" xlink:to="loc_dei_LegalEntityAxis_019dac15-a334-7cd4-a6a7-bc375009f839" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a334-7cd4-a6a7-bc375009f839_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a334-7cd4-a6a7-bc375009f839" xlink:to="loc_dei_EntityDomain_019dac15-a334-7cd4-a6a7-bc375009f839_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a334-74be-8799-1d87fde345c5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a334-7cd4-a6a7-bc375009f839" xlink:to="loc_dei_EntityDomain_019dac15-a334-74be-8799-1d87fde345c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CablevisionLightpathMember_019dac15-a334-7ad6-84d2-a983dccd6f5a" xlink:href="optu-20260331.xsd#optu_CablevisionLightpathMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a334-74be-8799-1d87fde345c5" xlink:to="loc_optu_CablevisionLightpathMember_019dac15-a334-7ad6-84d2-a983dccd6f5a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeAxis_019dac15-a334-7f32-ac35-44b7945296b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7f64-881b-d06f2ef0f6aa" xlink:to="loc_us-gaap_ShortTermDebtTypeAxis_019dac15-a334-7f32-ac35-44b7945296b2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-7f32-ac35-44b7945296b2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_019dac15-a334-7f32-ac35-44b7945296b2" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-7f32-ac35-44b7945296b2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-72a0-8655-2cbc27ab951f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_019dac15-a334-7f32-ac35-44b7945296b2" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-72a0-8655-2cbc27ab951f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansPayableMember_019dac15-a334-7a11-874b-d165d16a976b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoansPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-72a0-8655-2cbc27ab951f" xlink:to="loc_us-gaap_LoansPayableMember_019dac15-a334-7a11-874b-d165d16a976b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CreditFacilityMember_019dac15-a334-718f-a611-8a9646c83cf0" xlink:href="optu-20260331.xsd#optu_CreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-72a0-8655-2cbc27ab951f" xlink:to="loc_optu_CreditFacilityMember_019dac15-a334-718f-a611-8a9646c83cf0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtMember_019dac15-a334-757a-8f0f-3b170d6b7b50" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-72a0-8655-2cbc27ab951f" xlink:to="loc_us-gaap_ShortTermDebtMember_019dac15-a334-757a-8f0f-3b170d6b7b50" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_ReceivableFacilityLoanMember_019dac15-a334-771e-9112-f543af560781" xlink:href="optu-20260331.xsd#optu_ReceivableFacilityLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-72a0-8655-2cbc27ab951f" xlink:to="loc_optu_ReceivableFacilityLoanMember_019dac15-a334-771e-9112-f543af560781" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_019dac15-a334-70e1-9ff8-55bbc2b8e603" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7f64-881b-d06f2ef0f6aa" xlink:to="loc_us-gaap_VariableRateAxis_019dac15-a334-70e1-9ff8-55bbc2b8e603" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019dac15-a334-70e1-9ff8-55bbc2b8e603_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_019dac15-a334-70e1-9ff8-55bbc2b8e603" xlink:to="loc_us-gaap_VariableRateDomain_019dac15-a334-70e1-9ff8-55bbc2b8e603_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019dac15-a334-78c4-80c3-7290970d290d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_019dac15-a334-70e1-9ff8-55bbc2b8e603" xlink:to="loc_us-gaap_VariableRateDomain_019dac15-a334-78c4-80c3-7290970d290d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_AlternateBaseRateMember_019dac15-a334-7b9e-b63c-b213a02023cd" xlink:href="optu-20260331.xsd#optu_AlternateBaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019dac15-a334-78c4-80c3-7290970d290d" xlink:to="loc_optu_AlternateBaseRateMember_019dac15-a334-7b9e-b63c-b213a02023cd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_SyntheticLIBORMember_019dac15-a334-73ff-926f-fac15b2306af" xlink:href="optu-20260331.xsd#optu_SyntheticLIBORMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019dac15-a334-78c4-80c3-7290970d290d" xlink:to="loc_optu_SyntheticLIBORMember_019dac15-a334-73ff-926f-fac15b2306af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_FedRatePrimeRateAndAlternateBaseRateMember_019dac15-a334-7109-b613-4732ee7592c8" xlink:href="optu-20260331.xsd#optu_FedRatePrimeRateAndAlternateBaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019dac15-a334-78c4-80c3-7290970d290d" xlink:to="loc_optu_FedRatePrimeRateAndAlternateBaseRateMember_019dac15-a334-7109-b613-4732ee7592c8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_SyntheticLIBORRateOneMonthMember_019dac15-a334-7c6b-859a-d9ed3b9d70a0" xlink:href="optu-20260331.xsd#optu_SyntheticLIBORRateOneMonthMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019dac15-a334-78c4-80c3-7290970d290d" xlink:to="loc_optu_SyntheticLIBORRateOneMonthMember_019dac15-a334-7c6b-859a-d9ed3b9d70a0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_SyntheticLIBORRateThreeMonthsMember_019dac15-a334-7b9f-8f16-40067ee4a451" xlink:href="optu-20260331.xsd#optu_SyntheticLIBORRateThreeMonthsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019dac15-a334-78c4-80c3-7290970d290d" xlink:to="loc_optu_SyntheticLIBORRateThreeMonthsMember_019dac15-a334-7b9f-8f16-40067ee4a451" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_SyntheticLIBORRateSixMonthsMember_019dac15-a334-79f4-962e-3b39439b3ebd" xlink:href="optu-20260331.xsd#optu_SyntheticLIBORRateSixMonthsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019dac15-a334-78c4-80c3-7290970d290d" xlink:to="loc_optu_SyntheticLIBORRateSixMonthsMember_019dac15-a334-79f4-962e-3b39439b3ebd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019dac15-a334-7aa8-acaa-a424b98860a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019dac15-a334-78c4-80c3-7290970d290d" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019dac15-a334-7aa8-acaa-a424b98860a4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019dac15-a334-74e4-9aa6-7de7acf8b73f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019dac15-a334-74e4-9aa6-7de7acf8b73f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019dac15-a334-7867-8c0d-df48f4c8eb87" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019dac15-a334-7867-8c0d-df48f4c8eb87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotes_019dac15-a334-7155-a46b-f4628450a466" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_us-gaap_SeniorNotes_019dac15-a334-7155-a46b-f4628450a466" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_FaceAmountOfSeniorNotes_019dac15-a334-76a8-94f5-d1903aa8933b" xlink:href="optu-20260331.xsd#optu_FaceAmountOfSeniorNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_optu_FaceAmountOfSeniorNotes_019dac15-a334-76a8-94f5-d1903aa8933b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CarryingAmountOfSeniorNotes_019dac15-a334-776d-ad4a-4069bdb73527" xlink:href="optu-20260331.xsd#optu_CarryingAmountOfSeniorNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_optu_CarryingAmountOfSeniorNotes_019dac15-a334-776d-ad4a-4069bdb73527" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_FaceAmountOfSeniorGuaranteedNotes_019dac15-a334-75b9-abeb-30d3c30a02d5" xlink:href="optu-20260331.xsd#optu_FaceAmountOfSeniorGuaranteedNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_optu_FaceAmountOfSeniorGuaranteedNotes_019dac15-a334-75b9-abeb-30d3c30a02d5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CarryingAmountOfSeniorGuaranteedNotes_019dac15-a334-7bca-b7cc-cc6f93b17fd4" xlink:href="optu-20260331.xsd#optu_CarryingAmountOfSeniorGuaranteedNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_optu_CarryingAmountOfSeniorGuaranteedNotes_019dac15-a334-7bca-b7cc-cc6f93b17fd4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd_019dac15-a334-7383-a6e9-ad7283a4185c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd_019dac15-a334-7383-a6e9-ad7283a4185c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019dac15-a334-79e8-94a1-aec718a678ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_us-gaap_LineOfCredit_019dac15-a334-79e8-94a1-aec718a678ec" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_FaceAmountOfCreditFacilityDebt_019dac15-a334-7052-8751-0d34db04a025" xlink:href="optu-20260331.xsd#optu_FaceAmountOfCreditFacilityDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_optu_FaceAmountOfCreditFacilityDebt_019dac15-a334-7052-8751-0d34db04a025" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CarryingValueOfCreditFacilityDebt_019dac15-a334-7d5d-85cc-c1a1a8b5a34d" xlink:href="optu-20260331.xsd#optu_CarryingValueOfCreditFacilityDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_optu_CarryingValueOfCreditFacilityDebt_019dac15-a334-7d5d-85cc-c1a1a8b5a34d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_FaceAmountOfSeniorNotesAndSeniorSecuredNotes_019dac15-a334-7c8e-8580-76eed3b9f4b9" xlink:href="optu-20260331.xsd#optu_FaceAmountOfSeniorNotesAndSeniorSecuredNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_optu_FaceAmountOfSeniorNotesAndSeniorSecuredNotes_019dac15-a334-7c8e-8580-76eed3b9f4b9" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CarryingAmountOfSeniorNotesAndSeniorSecuredNotes_019dac15-a334-7ff5-994d-4d8a5f966852" xlink:href="optu-20260331.xsd#optu_CarryingAmountOfSeniorNotesAndSeniorSecuredNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_optu_CarryingAmountOfSeniorNotesAndSeniorSecuredNotes_019dac15-a334-7ff5-994d-4d8a5f966852" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesAtCarryingValue_019dac15-a334-7a06-8aa7-7badb1473618" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetBackedSecuritiesAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_us-gaap_AssetBackedSecuritiesAtCarryingValue_019dac15-a334-7a06-8aa7-7badb1473618" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiability_019dac15-a334-7f1c-9fcd-ce948b5a0d6c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinanceLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_us-gaap_FinanceLeaseLiability_019dac15-a334-7f1c-9fcd-ce948b5a0d6c" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019dac15-a334-7844-a1a1-2b7d0dd2350a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_us-gaap_LongTermDebt_019dac15-a334-7844-a1a1-2b7d0dd2350a" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilityCurrent_019dac15-a334-7b7a-b08c-703d78fdbebd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinanceLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_us-gaap_FinanceLeaseLiabilityCurrent_019dac15-a334-7b7a-b08c-703d78fdbebd" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_019dac15-a334-713c-964b-bf768d865687" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_us-gaap_LongTermDebtCurrent_019dac15-a334-713c-964b-bf768d865687" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019dac15-a334-742a-a244-50f2c062c3f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019dac15-a334-742a-a244-50f2c062c3f7" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_019dac15-a334-7976-94cf-ff168d3b8057" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_019dac15-a334-7976-94cf-ff168d3b8057" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_019dac15-a334-7e74-84bc-cbb008d70070" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_019dac15-a334-7e74-84bc-cbb008d70070" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019dac15-a334-7ca5-818a-1879b5695aff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019dac15-a334-7ca5-818a-1879b5695aff" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019dac15-a334-708e-8f0d-270b826e5b9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019dac15-a334-708e-8f0d-270b826e5b9f" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityPeriodicPaymentPrincipal_019dac15-a334-7e6a-a906-e2dec7a36d03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityPeriodicPaymentPrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7b19-aada-7a48592a2a89" xlink:to="loc_us-gaap_LineOfCreditFacilityPeriodicPaymentPrincipal_019dac15-a334-7e6a-a906-e2dec7a36d03" xlink:type="arc" order="23"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/DEBTSeniorGuaranteedNotesSeniorSecuredNotesandSeniorNotesandDebenturesDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#DEBTSeniorGuaranteedNotesSeniorSecuredNotesandSeniorNotesandDebenturesDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/DEBTSeniorGuaranteedNotesSeniorSecuredNotesandSeniorNotesandDebenturesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7848-81f7-429cd801b8d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019dac15-a334-72f2-80e0-6959ea7e132e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7848-81f7-429cd801b8d3" xlink:to="loc_us-gaap_DebtInstrumentTable_019dac15-a334-72f2-80e0-6959ea7e132e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-7577-b5f7-bbf6ff18bdb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-72f2-80e0-6959ea7e132e" xlink:to="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-7577-b5f7-bbf6ff18bdb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7577-b5f7-bbf6ff18bdb3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-7577-b5f7-bbf6ff18bdb3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7577-b5f7-bbf6ff18bdb3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-718f-8ef3-1f7d3f6faf04" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-7577-b5f7-bbf6ff18bdb3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-718f-8ef3-1f7d3f6faf04" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_SupplyChainFinancingMember_019dac15-a334-736b-8de2-c97228c945a1" xlink:href="optu-20260331.xsd#optu_SupplyChainFinancingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-718f-8ef3-1f7d3f6faf04" xlink:to="loc_optu_SupplyChainFinancingMember_019dac15-a334-736b-8de2-c97228c945a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_IncrementalTermLoanB5Member_019de43a-d69c-7dda-86b8-b4158c627099" xlink:href="optu-20260331.xsd#optu_IncrementalTermLoanB5Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-718f-8ef3-1f7d3f6faf04" xlink:to="loc_optu_IncrementalTermLoanB5Member_019de43a-d69c-7dda-86b8-b4158c627099" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_UnsubGroupCreditFacilityMember_019de43b-e160-7bf7-8061-01ab7dcd742c" xlink:href="optu-20260331.xsd#optu_UnsubGroupCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-718f-8ef3-1f7d3f6faf04" xlink:to="loc_optu_UnsubGroupCreditFacilityMember_019de43b-e160-7bf7-8061-01ab7dcd742c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorSubordinatedNotesMember_019de43e-070c-79c9-b875-083eed7dccba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorSubordinatedNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-718f-8ef3-1f7d3f6faf04" xlink:to="loc_us-gaap_SeniorSubordinatedNotesMember_019de43e-070c-79c9-b875-083eed7dccba" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_NYCABSReceivableFacilityLoanMember_019de43e-c8c6-7717-b997-115f8b48e343" xlink:href="optu-20260331.xsd#optu_NYCABSReceivableFacilityLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-718f-8ef3-1f7d3f6faf04" xlink:to="loc_optu_NYCABSReceivableFacilityLoanMember_019de43e-c8c6-7717-b997-115f8b48e343" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CablevisionLightpathLLC3875NotesDueSeptember152027Member_019de440-bb6a-75da-a041-493efd7f6c64" xlink:href="optu-20260331.xsd#optu_CablevisionLightpathLLC3875NotesDueSeptember152027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-718f-8ef3-1f7d3f6faf04" xlink:to="loc_optu_CablevisionLightpathLLC3875NotesDueSeptember152027Member_019de440-bb6a-75da-a041-493efd7f6c64" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_LightpathFiberIssuerLLCSeries20261ClassA25.597NotesDue2031Member_019de444-6552-77f6-9210-64630edce15e" xlink:href="optu-20260331.xsd#optu_LightpathFiberIssuerLLCSeries20261ClassA25.597NotesDue2031Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-718f-8ef3-1f7d3f6faf04" xlink:to="loc_optu_LightpathFiberIssuerLLCSeries20261ClassA25.597NotesDue2031Member_019de444-6552-77f6-9210-64630edce15e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_LightpathFiberIssuerLLCSeries20261ClassB5.597NotesDue2031Member_019de447-57c9-7d2f-b45f-94c1d7cc3c29" xlink:href="optu-20260331.xsd#optu_LightpathFiberIssuerLLCSeries20261ClassB5.597NotesDue2031Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-718f-8ef3-1f7d3f6faf04" xlink:to="loc_optu_LightpathFiberIssuerLLCSeries20261ClassB5.597NotesDue2031Member_019de447-57c9-7d2f-b45f-94c1d7cc3c29" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_SecuredFiberNetworkRevenueNotesMember_019de448-609c-7ea8-9d37-e41dd0b0dd95" xlink:href="optu-20260331.xsd#optu_SecuredFiberNetworkRevenueNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-718f-8ef3-1f7d3f6faf04" xlink:to="loc_optu_SecuredFiberNetworkRevenueNotesMember_019de448-609c-7ea8-9d37-e41dd0b0dd95" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_LightpathVariableFundingNotesMember_019de449-82cc-7e0a-b78c-58ec4d46ed63" xlink:href="optu-20260331.xsd#optu_LightpathVariableFundingNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-718f-8ef3-1f7d3f6faf04" xlink:to="loc_optu_LightpathVariableFundingNotesMember_019de449-82cc-7e0a-b78c-58ec4d46ed63" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsRevolvingCreditFacilityMember_019de449-e029-72e2-96f7-a045561336b5" xlink:href="optu-20260331.xsd#optu_CSCHoldingsRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-718f-8ef3-1f7d3f6faf04" xlink:to="loc_optu_CSCHoldingsRevolvingCreditFacilityMember_019de449-e029-72e2-96f7-a045561336b5" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeAxis_019dac15-a334-78ac-832b-0a068430bdcc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-72f2-80e0-6959ea7e132e" xlink:to="loc_us-gaap_ShortTermDebtTypeAxis_019dac15-a334-78ac-832b-0a068430bdcc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-78ac-832b-0a068430bdcc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_019dac15-a334-78ac-832b-0a068430bdcc" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-78ac-832b-0a068430bdcc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-7930-bb80-514245ed04a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_019dac15-a334-78ac-832b-0a068430bdcc" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-7930-bb80-514245ed04a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_ReceivableFacilityLoanMember_019dac15-a334-79f3-b154-64c9380f7315" xlink:href="optu-20260331.xsd#optu_ReceivableFacilityLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-7930-bb80-514245ed04a8" xlink:to="loc_optu_ReceivableFacilityLoanMember_019dac15-a334-79f3-b154-64c9380f7315" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CreditFacilityMember_019dac15-a334-7a66-a977-dbb1b1e564c8" xlink:href="optu-20260331.xsd#optu_CreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-7930-bb80-514245ed04a8" xlink:to="loc_optu_CreditFacilityMember_019dac15-a334-7a66-a977-dbb1b1e564c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansPayableMember_019de3c2-563a-77d9-b4f2-211ebf918ddb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoansPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-7930-bb80-514245ed04a8" xlink:to="loc_us-gaap_LoansPayableMember_019de3c2-563a-77d9-b4f2-211ebf918ddb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019de43a-d69c-70a8-bd7c-eae20134768a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-72f2-80e0-6959ea7e132e" xlink:to="loc_us-gaap_CreditFacilityAxis_019de43a-d69c-70a8-bd7c-eae20134768a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019de43a-d69c-70a8-bd7c-eae20134768a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019de43a-d69c-70a8-bd7c-eae20134768a" xlink:to="loc_us-gaap_CreditFacilityDomain_019de43a-d69c-70a8-bd7c-eae20134768a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019de43a-d69c-700f-a340-a12f4d04cba3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019de43a-d69c-70a8-bd7c-eae20134768a" xlink:to="loc_us-gaap_CreditFacilityDomain_019de43a-d69c-700f-a340-a12f4d04cba3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019de43a-d69c-75fb-b077-a3903b6f2055" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019de43a-d69c-700f-a340-a12f4d04cba3" xlink:to="loc_us-gaap_SecuredDebtMember_019de43a-d69c-75fb-b077-a3903b6f2055" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorSubordinatedNotesMember_019de43d-dc34-7b00-a25c-5df71abd39de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorSubordinatedNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019de43a-d69c-700f-a340-a12f4d04cba3" xlink:to="loc_us-gaap_SeniorSubordinatedNotesMember_019de43d-dc34-7b00-a25c-5df71abd39de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019de449-e029-75fa-b19e-8095c3529fa2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019de43a-d69c-700f-a340-a12f4d04cba3" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019de449-e029-75fa-b19e-8095c3529fa2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019de43c-df0b-711c-b8d5-7c4f2277255c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-72f2-80e0-6959ea7e132e" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019de43c-df0b-711c-b8d5-7c4f2277255c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019de43c-df0b-711c-b8d5-7c4f2277255c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019de43c-df0b-711c-b8d5-7c4f2277255c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019de43c-df0b-711c-b8d5-7c4f2277255c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019de43c-df0b-74a7-87cd-130d239e98e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019de43c-df0b-711c-b8d5-7c4f2277255c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019de43c-df0b-74a7-87cd-130d239e98e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorSubordinatedNotesMember_019de43c-df0b-7638-84b0-c5c68cf99195" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorSubordinatedNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019de43c-df0b-74a7-87cd-130d239e98e1" xlink:to="loc_us-gaap_SeniorSubordinatedNotesMember_019de43c-df0b-7638-84b0-c5c68cf99195" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019de440-bb6a-7b52-bb8f-0c8e47eeee07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019de43c-df0b-74a7-87cd-130d239e98e1" xlink:to="loc_us-gaap_SecuredDebtMember_019de440-bb6a-7b52-bb8f-0c8e47eeee07" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019dac15-a334-73eb-b334-acdc2cf87613" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7848-81f7-429cd801b8d3" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019dac15-a334-73eb-b334-acdc2cf87613" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_019dac15-a334-7dbd-814e-715cef3554a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7848-81f7-429cd801b8d3" xlink:to="loc_us-gaap_LongTermDebtCurrent_019dac15-a334-7dbd-814e-715cef3554a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019de3c2-563a-7596-8586-3727db6b985e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7848-81f7-429cd801b8d3" xlink:to="loc_us-gaap_LongTermDebt_019de3c2-563a-7596-8586-3727db6b985e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019de43c-0ca4-714e-9be7-4cf5e5062315" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7848-81f7-429cd801b8d3" xlink:to="loc_us-gaap_LineOfCredit_019de43c-0ca4-714e-9be7-4cf5e5062315" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd_019de43f-fe37-7bab-abab-6dae5fdda908" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7848-81f7-429cd801b8d3" xlink:to="loc_us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd_019de43f-fe37-7bab-abab-6dae5fdda908" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019de440-bb6a-70ab-be95-24fa7389c786" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7848-81f7-429cd801b8d3" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019de440-bb6a-70ab-be95-24fa7389c786" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_019de449-82cc-7b97-8272-4431d8d15625" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7848-81f7-429cd801b8d3" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_019de449-82cc-7b97-8272-4431d8d15625" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019de449-e029-7e43-bde3-c43b71514544" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7848-81f7-429cd801b8d3" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019de449-e029-7e43-bde3-c43b71514544" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_019de44c-3b64-7cbf-9646-c527958faf37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7848-81f7-429cd801b8d3" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_019de44c-3b64-7cbf-9646-c527958faf37" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/DEBTScheduleofGainLossonDebtExtinguishmentDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#DEBTScheduleofGainLossonDebtExtinguishmentDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/DEBTScheduleofGainLossonDebtExtinguishmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7880-9e91-4837918d623a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7cc9-87df-0adf1b1e9fcf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7880-9e91-4837918d623a" xlink:to="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7cc9-87df-0adf1b1e9fcf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-7806-9a7d-d28df65355e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7cc9-87df-0adf1b1e9fcf" xlink:to="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-7806-9a7d-d28df65355e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7806-9a7d-d28df65355e2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-7806-9a7d-d28df65355e2" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7806-9a7d-d28df65355e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-7806-9a7d-d28df65355e2" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_Cablevision7.75NotesdueApril152018Member_019dac15-a334-7e1f-8036-8656bfa267f4" xlink:href="optu-20260331.xsd#optu_Cablevision7.75NotesdueApril152018Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_Cablevision7.75NotesdueApril152018Member_019dac15-a334-7e1f-8036-8656bfa267f4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CequelandCequelCapital6.375SeniorNotesdueSeptember152020Member_019dac15-a334-7a42-9d5b-0f0e68883992" xlink:href="optu-20260331.xsd#optu_CequelandCequelCapital6.375SeniorNotesdueSeptember152020Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_CequelandCequelCapital6.375SeniorNotesdueSeptember152020Member_019dac15-a334-7a42-9d5b-0f0e68883992" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CequelCreditFacilitiesMember_019dac15-a334-7564-90df-3c529455147a" xlink:href="optu-20260331.xsd#optu_CequelCreditFacilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_CequelCreditFacilitiesMember_019dac15-a334-7564-90df-3c529455147a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_ExchangeOfferMember_019dac15-a334-7d6a-a937-53cb62f80b68" xlink:href="optu-20260331.xsd#optu_ExchangeOfferMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_ExchangeOfferMember_019dac15-a334-7d6a-a937-53cb62f80b68" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_NotesPayabletoAffiliatesMember_019dac15-a334-7c71-8b76-5d0298b321f3" xlink:href="optu-20260331.xsd#optu_NotesPayabletoAffiliatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_NotesPayabletoAffiliatesMember_019dac15-a334-7c71-8b76-5d0298b321f3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsTermLoanBMember_019dac15-a334-7234-a282-c14472d3b19c" xlink:href="optu-20260331.xsd#optu_CSCHoldingsTermLoanBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_CSCHoldingsTermLoanBMember_019dac15-a334-7234-a282-c14472d3b19c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldings10.875NotesdueOctober152025Member_019dac15-a334-781b-a9d9-91341e1c8d09" xlink:href="optu-20260331.xsd#optu_CSCHoldings10.875NotesdueOctober152025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_CSCHoldings10.875NotesdueOctober152025Member_019dac15-a334-781b-a9d9-91341e1c8d09" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldings8.625NotesdueSeptember152017Member_019dac15-a334-7319-be47-3f3ac380fa7b" xlink:href="optu-20260331.xsd#optu_CSCHoldings8.625NotesdueSeptember152017Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_CSCHoldings8.625NotesdueSeptember152017Member_019dac15-a334-7319-be47-3f3ac380fa7b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CequelTermLoanFacilityMember_019dac15-a334-7073-8528-9edcc06b9f5b" xlink:href="optu-20260331.xsd#optu_CequelTermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_CequelTermLoanFacilityMember_019dac15-a334-7073-8528-9edcc06b9f5b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_Cequel6.375SeniorNotesdue2020Member_019dac15-a334-7646-8548-884c10a83193" xlink:href="optu-20260331.xsd#optu_Cequel6.375SeniorNotesdue2020Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_Cequel6.375SeniorNotesdue2020Member_019dac15-a334-7646-8548-884c10a83193" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_Cablevision8.0NotesdueApril152020Member_019dac15-a334-788c-9f28-a7bb5dd9d8b3" xlink:href="optu-20260331.xsd#optu_Cablevision8.0NotesdueApril152020Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_Cablevision8.0NotesdueApril152020Member_019dac15-a334-788c-9f28-a7bb5dd9d8b3" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsCablevision5125NotesDueDecember152021Member_019dac15-a334-7521-a2a7-4b0550351b94" xlink:href="optu-20260331.xsd#optu_CSCHoldingsCablevision5125NotesDueDecember152021Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_CSCHoldingsCablevision5125NotesDueDecember152021Member_019dac15-a334-7521-a2a7-4b0550351b94" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldings5.125NotesdueDecember152021Member_019dac15-a334-7b60-9e42-75e0e353d76d" xlink:href="optu-20260331.xsd#optu_CSCHoldings5.125NotesdueDecember152021Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_CSCHoldings5.125NotesdueDecember152021Member_019dac15-a334-7b60-9e42-75e0e353d76d" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldings10.125NotesdueJanuary152023Member_019dac15-a334-7faa-81a6-6075e6d9bd49" xlink:href="optu-20260331.xsd#optu_CSCHoldings10.125NotesdueJanuary152023Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_CSCHoldings10.125NotesdueJanuary152023Member_019dac15-a334-7faa-81a6-6075e6d9bd49" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsTermLoanFacilityMember_019dac15-a334-7ccd-911f-f9819e006044" xlink:href="optu-20260331.xsd#optu_CSCHoldingsTermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_CSCHoldingsTermLoanFacilityMember_019dac15-a334-7ccd-911f-f9819e006044" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CequelNotesRelatingToDebtExchangeMember_019dac15-a334-7272-af08-698b28a99750" xlink:href="optu-20260331.xsd#optu_CequelNotesRelatingToDebtExchangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_CequelNotesRelatingToDebtExchangeMember_019dac15-a334-7272-af08-698b28a99750" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CablevisionHoldings8.625NotesdueSeptember152017Member_019dac15-a334-7bce-905c-9b3484ddd48c" xlink:href="optu-20260331.xsd#optu_CablevisionHoldings8.625NotesdueSeptember152017Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_CablevisionHoldings8.625NotesdueSeptember152017Member_019dac15-a334-7bce-905c-9b3484ddd48c" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_NYCABSReceivableFacilityLoanMember_019de456-92f9-73b6-a0b8-3d2d5d728402" xlink:href="optu-20260331.xsd#optu_NYCABSReceivableFacilityLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_NYCABSReceivableFacilityLoanMember_019de456-92f9-73b6-a0b8-3d2d5d728402" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_LightpathCreditFacilitySeniorSecuredAndSeniorNotesMember_019de457-d4f8-74db-bae9-7505ea989017" xlink:href="optu-20260331.xsd#optu_LightpathCreditFacilitySeniorSecuredAndSeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-74f8-a826-bb02029e5016" xlink:to="loc_optu_LightpathCreditFacilitySeniorSecuredAndSeniorNotesMember_019de457-d4f8-74db-bae9-7505ea989017" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a334-702e-9d30-c83f9da69782" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7cc9-87df-0adf1b1e9fcf" xlink:to="loc_dei_LegalEntityAxis_019dac15-a334-702e-9d30-c83f9da69782" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a334-702e-9d30-c83f9da69782_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a334-702e-9d30-c83f9da69782" xlink:to="loc_dei_EntityDomain_019dac15-a334-702e-9d30-c83f9da69782_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a334-794f-b5c7-7d190d7b0015" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a334-702e-9d30-c83f9da69782" xlink:to="loc_dei_EntityDomain_019dac15-a334-794f-b5c7-7d190d7b0015" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsMember_019dac15-a334-7af6-aeab-783ae294be25" xlink:href="optu-20260331.xsd#optu_CSCHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a334-794f-b5c7-7d190d7b0015" xlink:to="loc_optu_CSCHoldingsMember_019dac15-a334-7af6-aeab-783ae294be25" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CablevisionSystemsCorp.Member_019dac15-a334-73ed-b4a7-4ea043a4fe7a" xlink:href="optu-20260331.xsd#optu_CablevisionSystemsCorp.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a334-794f-b5c7-7d190d7b0015" xlink:to="loc_optu_CablevisionSystemsCorp.Member_019dac15-a334-73ed-b4a7-4ea043a4fe7a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_AlticeUSAMember_019dac15-a334-727f-99f1-105906019180" xlink:href="optu-20260331.xsd#optu_AlticeUSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a334-794f-b5c7-7d190d7b0015" xlink:to="loc_optu_AlticeUSAMember_019dac15-a334-727f-99f1-105906019180" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019de456-92f9-763d-8e6e-029d88069a1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7cc9-87df-0adf1b1e9fcf" xlink:to="loc_us-gaap_CreditFacilityAxis_019de456-92f9-763d-8e6e-029d88069a1f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019de456-92f9-763d-8e6e-029d88069a1f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019de456-92f9-763d-8e6e-029d88069a1f" xlink:to="loc_us-gaap_CreditFacilityDomain_019de456-92f9-763d-8e6e-029d88069a1f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019de456-92f9-7a90-9207-97fbd89f84dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019de456-92f9-763d-8e6e-029d88069a1f" xlink:to="loc_us-gaap_CreditFacilityDomain_019de456-92f9-7a90-9207-97fbd89f84dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019de456-92f9-7c3a-a2bb-a62320df1bcb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019de456-92f9-7a90-9207-97fbd89f84dc" xlink:to="loc_us-gaap_SecuredDebtMember_019de456-92f9-7c3a-a2bb-a62320df1bcb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019dac15-a334-7f2a-9b86-bb08ac5a3fdc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7880-9e91-4837918d623a" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019dac15-a334-7f2a-9b86-bb08ac5a3fdc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019dac15-a334-72b1-aab3-9259667b2204" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/DEBTABSDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#DEBTABSDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/DEBTABSDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-78db-82b2-6d81d6a878f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7dd0-a37a-dcede357e086" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-78db-82b2-6d81d6a878f8" xlink:to="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7dd0-a37a-dcede357e086" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-700b-b4d7-e8a19d7ed808" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7dd0-a37a-dcede357e086" xlink:to="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-700b-b4d7-e8a19d7ed808" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-700b-b4d7-e8a19d7ed808_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-700b-b4d7-e8a19d7ed808" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-700b-b4d7-e8a19d7ed808_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73d5-8f52-b39fe85acc5a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-700b-b4d7-e8a19d7ed808" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73d5-8f52-b39fe85acc5a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_ReceivableFacilityLoanMember_019dac15-a334-721e-91df-f15f3600b31f" xlink:href="optu-20260331.xsd#optu_ReceivableFacilityLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73d5-8f52-b39fe85acc5a" xlink:to="loc_optu_ReceivableFacilityLoanMember_019dac15-a334-721e-91df-f15f3600b31f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CollateralPledgedPaymentsUpThroughJanuary162028Member_019dac15-a334-7514-9f53-693d7eac8ac9" xlink:href="optu-20260331.xsd#optu_CollateralPledgedPaymentsUpThroughJanuary162028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73d5-8f52-b39fe85acc5a" xlink:to="loc_optu_CollateralPledgedPaymentsUpThroughJanuary162028Member_019dac15-a334-7514-9f53-693d7eac8ac9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CollateralPledgedPaymentsAfterJanuary162028Member_019dac15-a334-756d-a4e8-9f3ac3450495" xlink:href="optu-20260331.xsd#optu_CollateralPledgedPaymentsAfterJanuary162028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-73d5-8f52-b39fe85acc5a" xlink:to="loc_optu_CollateralPledgedPaymentsAfterJanuary162028Member_019dac15-a334-756d-a4e8-9f3ac3450495" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019dac15-a334-713a-a2e5-fe25475d6308" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-78db-82b2-6d81d6a878f8" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019dac15-a334-713a-a2e5-fe25475d6308" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscount_019dac15-a334-7206-84a4-76468ea640e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentUnamortizedDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-78db-82b2-6d81d6a878f8" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscount_019dac15-a334-7206-84a4-76468ea640e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019dac15-a334-789e-ad06-18fc0f6b7efe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-78db-82b2-6d81d6a878f8" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019dac15-a334-789e-ad06-18fc0f6b7efe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentPeriodicPaymentPrincipal_019dac15-a334-733d-9b52-2017c55a58a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentPeriodicPaymentPrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-78db-82b2-6d81d6a878f8" xlink:to="loc_us-gaap_DebtInstrumentPeriodicPaymentPrincipal_019dac15-a334-733d-9b52-2017c55a58a3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDebtNetOfIssuanceCosts_019dac15-a334-7f90-9e5d-8e492595acae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromDebtNetOfIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-78db-82b2-6d81d6a878f8" xlink:to="loc_us-gaap_ProceedsFromDebtNetOfIssuanceCosts_019dac15-a334-7f90-9e5d-8e492595acae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashCurrent_019dac15-a334-7d91-910c-0391c2d5c6e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-78db-82b2-6d81d6a878f8" xlink:to="loc_us-gaap_RestrictedCashCurrent_019dac15-a334-7d91-910c-0391c2d5c6e4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndInvestmentsNoncurrent_019dac15-a334-7c5a-831e-edbf08048c4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndInvestmentsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-78db-82b2-6d81d6a878f8" xlink:to="loc_us-gaap_RestrictedCashAndInvestmentsNoncurrent_019dac15-a334-7c5a-831e-edbf08048c4e" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/DEBTNarrativeDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#DEBTNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/DEBTNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7e84-9777-7b4b8fd7b8a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7aaf-b81e-35548a355eee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7e84-9777-7b4b8fd7b8a9" xlink:to="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7aaf-b81e-35548a355eee" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019dac15-a334-7cff-b7e1-5abaa051cad9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7aaf-b81e-35548a355eee" xlink:to="loc_us-gaap_CreditFacilityAxis_019dac15-a334-7cff-b7e1-5abaa051cad9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019dac15-a334-7cff-b7e1-5abaa051cad9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019dac15-a334-7cff-b7e1-5abaa051cad9" xlink:to="loc_us-gaap_CreditFacilityDomain_019dac15-a334-7cff-b7e1-5abaa051cad9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019dac15-a334-7e3a-b704-f8a80dcef923" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019dac15-a334-7cff-b7e1-5abaa051cad9" xlink:to="loc_us-gaap_CreditFacilityDomain_019dac15-a334-7e3a-b704-f8a80dcef923" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019dac15-a334-7431-9483-8e541d3929f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019dac15-a334-7e3a-b704-f8a80dcef923" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019dac15-a334-7431-9483-8e541d3929f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019dac15-a334-7a73-a0aa-f0ace9814f7d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019dac15-a334-7e3a-b704-f8a80dcef923" xlink:to="loc_us-gaap_SecuredDebtMember_019dac15-a334-7a73-a0aa-f0ace9814f7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CablevisionLightpathRevolvingCreditFacilityMember_019dac15-a334-781d-8dec-1a533c02590e" xlink:href="optu-20260331.xsd#optu_CablevisionLightpathRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019dac15-a334-7e3a-b704-f8a80dcef923" xlink:to="loc_optu_CablevisionLightpathRevolvingCreditFacilityMember_019dac15-a334-781d-8dec-1a533c02590e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-7fd9-b71a-62921cf4eef2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7aaf-b81e-35548a355eee" xlink:to="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-7fd9-b71a-62921cf4eef2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7fd9-b71a-62921cf4eef2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-7fd9-b71a-62921cf4eef2" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7fd9-b71a-62921cf4eef2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-7fd9-b71a-62921cf4eef2" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsRevolvingCreditFacilityMember_019dac15-a334-75e3-be0d-a369aad3ed45" xlink:href="optu-20260331.xsd#optu_CSCHoldingsRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:to="loc_optu_CSCHoldingsRevolvingCreditFacilityMember_019dac15-a334-75e3-be0d-a369aad3ed45" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldings11.7500SeniorGuaranteedNotesDueJan312029Member_019dac15-a334-7709-83dc-24b1b2cab20c" xlink:href="optu-20260331.xsd#optu_CSCHoldings11.7500SeniorGuaranteedNotesDueJan312029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:to="loc_optu_CSCHoldings11.7500SeniorGuaranteedNotesDueJan312029Member_019dac15-a334-7709-83dc-24b1b2cab20c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CablevisionLightpathRevolvingCreditFacilityMember_019dac15-a334-7ab7-b26b-e5a77ec07d2d" xlink:href="optu-20260331.xsd#optu_CablevisionLightpathRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:to="loc_optu_CablevisionLightpathRevolvingCreditFacilityMember_019dac15-a334-7ab7-b26b-e5a77ec07d2d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CablevisionLightpathTermBLoanMember_019dac15-a334-7856-a6eb-7fbfa89b8c3c" xlink:href="optu-20260331.xsd#optu_CablevisionLightpathTermBLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:to="loc_optu_CablevisionLightpathTermBLoanMember_019dac15-a334-7856-a6eb-7fbfa89b8c3c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CablevisionLightpathTermBLoanRefinancingAmendmentMember_019dac15-a334-7b40-81e1-7b41975a13a3" xlink:href="optu-20260331.xsd#optu_CablevisionLightpathTermBLoanRefinancingAmendmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:to="loc_optu_CablevisionLightpathTermBLoanRefinancingAmendmentMember_019dac15-a334-7b40-81e1-7b41975a13a3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_IncrementalTermLoanB5Member_019dac15-a334-793c-bc73-6542c935a09f" xlink:href="optu-20260331.xsd#optu_IncrementalTermLoanB5Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:to="loc_optu_IncrementalTermLoanB5Member_019dac15-a334-793c-bc73-6542c935a09f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_ReceivableFacilityLoanMember_019dac15-a334-7c87-88da-651ba8a999da" xlink:href="optu-20260331.xsd#optu_ReceivableFacilityLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:to="loc_optu_ReceivableFacilityLoanMember_019dac15-a334-7c87-88da-651ba8a999da" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CollateralPledgedPaymentsAfterJanuary162028Member_019dac15-a334-74a0-ae3f-b95f478a228e" xlink:href="optu-20260331.xsd#optu_CollateralPledgedPaymentsAfterJanuary162028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:to="loc_optu_CollateralPledgedPaymentsAfterJanuary162028Member_019dac15-a334-74a0-ae3f-b95f478a228e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CollateralPledgedPaymentsUpThroughJanuary162028Member_019dac15-a334-725f-8ddf-872dc33c6546" xlink:href="optu-20260331.xsd#optu_CollateralPledgedPaymentsUpThroughJanuary162028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:to="loc_optu_CollateralPledgedPaymentsUpThroughJanuary162028Member_019dac15-a334-725f-8ddf-872dc33c6546" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_UnsubGroupCreditFacilityMember_019de473-78e4-7810-b8fd-f0edc3f10fa5" xlink:href="optu-20260331.xsd#optu_UnsubGroupCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:to="loc_optu_UnsubGroupCreditFacilityMember_019de473-78e4-7810-b8fd-f0edc3f10fa5" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_IncrementalUnsubGroupCreditFacilityMember_019de474-41d4-7709-8b58-1ac74d17383b" xlink:href="optu-20260331.xsd#optu_IncrementalUnsubGroupCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:to="loc_optu_IncrementalUnsubGroupCreditFacilityMember_019de474-41d4-7709-8b58-1ac74d17383b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_LightpathFiberIssuerLLCSeries20261ClassA25.597NotesDue2031Member_019de475-ad59-734a-81b9-dbe928466ae8" xlink:href="optu-20260331.xsd#optu_LightpathFiberIssuerLLCSeries20261ClassA25.597NotesDue2031Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:to="loc_optu_LightpathFiberIssuerLLCSeries20261ClassA25.597NotesDue2031Member_019de475-ad59-734a-81b9-dbe928466ae8" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_LightpathFiberIssuerLLCSeries20261ClassB5.597NotesDue2031Member_019de475-f28c-7a59-a85a-fef5b1feb6d3" xlink:href="optu-20260331.xsd#optu_LightpathFiberIssuerLLCSeries20261ClassB5.597NotesDue2031Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:to="loc_optu_LightpathFiberIssuerLLCSeries20261ClassB5.597NotesDue2031Member_019de475-f28c-7a59-a85a-fef5b1feb6d3" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_SecuredFiberNetworkRevenueNotesMember_019de478-7203-7a50-b942-3e1edf33a865" xlink:href="optu-20260331.xsd#optu_SecuredFiberNetworkRevenueNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:to="loc_optu_SecuredFiberNetworkRevenueNotesMember_019de478-7203-7a50-b942-3e1edf33a865" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_LightpathVariableFundingNotesMember_019de478-e340-7dab-b0a4-42da738170c6" xlink:href="optu-20260331.xsd#optu_LightpathVariableFundingNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:to="loc_optu_LightpathVariableFundingNotesMember_019de478-e340-7dab-b0a4-42da738170c6" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_LightpathLiquidityFundingNotesMember_019de47d-54f4-7e1d-97e1-b07446f46965" xlink:href="optu-20260331.xsd#optu_LightpathLiquidityFundingNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7a37-ba6f-f126e870e546" xlink:to="loc_optu_LightpathLiquidityFundingNotesMember_019de47d-54f4-7e1d-97e1-b07446f46965" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-756d-974f-309b5abb48be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7aaf-b81e-35548a355eee" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-756d-974f-309b5abb48be" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-756d-974f-309b5abb48be_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-756d-974f-309b5abb48be" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-756d-974f-309b5abb48be_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-77b8-9191-80d053c73356" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-756d-974f-309b5abb48be" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-77b8-9191-80d053c73356" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019dac15-a334-799d-a734-64987959fa6a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-77b8-9191-80d053c73356" xlink:to="loc_us-gaap_SecuredDebtMember_019dac15-a334-799d-a734-64987959fa6a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_019dac15-a334-7f82-88df-c0a50393bc6d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7aaf-b81e-35548a355eee" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_019dac15-a334-7f82-88df-c0a50393bc6d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019dac15-a334-7f82-88df-c0a50393bc6d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_019dac15-a334-7f82-88df-c0a50393bc6d" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019dac15-a334-7f82-88df-c0a50393bc6d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019dac15-a334-7524-bb78-c63b52ef089b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_019dac15-a334-7f82-88df-c0a50393bc6d" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019dac15-a334-7524-bb78-c63b52ef089b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_A2027RevolvingCreditCommitmentsMember_019dac15-a334-7b03-9568-454c4ec680f6" xlink:href="optu-20260331.xsd#optu_A2027RevolvingCreditCommitmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019dac15-a334-7524-bb78-c63b52ef089b" xlink:to="loc_optu_A2027RevolvingCreditCommitmentsMember_019dac15-a334-7b03-9568-454c4ec680f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_A2025RevolvingCreditCommitmentsMember_019dac15-a334-7664-acf9-c0ca5729b604" xlink:href="optu-20260331.xsd#optu_A2025RevolvingCreditCommitmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019dac15-a334-7524-bb78-c63b52ef089b" xlink:to="loc_optu_A2025RevolvingCreditCommitmentsMember_019dac15-a334-7664-acf9-c0ca5729b604" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_019dac15-a334-7aef-800b-87c17123ae47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7aaf-b81e-35548a355eee" xlink:to="loc_us-gaap_VariableRateAxis_019dac15-a334-7aef-800b-87c17123ae47" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019dac15-a334-7aef-800b-87c17123ae47_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_019dac15-a334-7aef-800b-87c17123ae47" xlink:to="loc_us-gaap_VariableRateDomain_019dac15-a334-7aef-800b-87c17123ae47_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019dac15-a334-72ef-b264-e8ea407406bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_019dac15-a334-7aef-800b-87c17123ae47" xlink:to="loc_us-gaap_VariableRateDomain_019dac15-a334-72ef-b264-e8ea407406bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_AlternateBaseRateMember_019dac15-a334-7745-ae10-f6ca75fe3d94" xlink:href="optu-20260331.xsd#optu_AlternateBaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019dac15-a334-72ef-b264-e8ea407406bc" xlink:to="loc_optu_AlternateBaseRateMember_019dac15-a334-7745-ae10-f6ca75fe3d94" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019dac15-a334-78ee-855e-d69ca7e647ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019dac15-a334-72ef-b264-e8ea407406bc" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019dac15-a334-78ee-855e-d69ca7e647ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_SyntheticLIBORRateOneMonthMember_019dac15-a334-7853-a054-607d20cbc640" xlink:href="optu-20260331.xsd#optu_SyntheticLIBORRateOneMonthMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019dac15-a334-72ef-b264-e8ea407406bc" xlink:to="loc_optu_SyntheticLIBORRateOneMonthMember_019dac15-a334-7853-a054-607d20cbc640" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_SyntheticLIBORRateThreeMonthsMember_019dac15-a334-73d3-b662-8a9a61676182" xlink:href="optu-20260331.xsd#optu_SyntheticLIBORRateThreeMonthsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019dac15-a334-72ef-b264-e8ea407406bc" xlink:to="loc_optu_SyntheticLIBORRateThreeMonthsMember_019dac15-a334-73d3-b662-8a9a61676182" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_SyntheticLIBORRateSixMonthsMember_019dac15-a334-776a-a444-4ad68c902011" xlink:href="optu-20260331.xsd#optu_SyntheticLIBORRateSixMonthsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019dac15-a334-72ef-b264-e8ea407406bc" xlink:to="loc_optu_SyntheticLIBORRateSixMonthsMember_019dac15-a334-776a-a444-4ad68c902011" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_SyntheticLIBORMember_019dac15-a334-7cae-8a26-a519be53a353" xlink:href="optu-20260331.xsd#optu_SyntheticLIBORMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019dac15-a334-72ef-b264-e8ea407406bc" xlink:to="loc_optu_SyntheticLIBORMember_019dac15-a334-7cae-8a26-a519be53a353" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_019dac15-a334-73c3-ab78-e6e2a6135478" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7e84-9777-7b4b8fd7b8a9" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_019dac15-a334-73c3-ab78-e6e2a6135478" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_019dac15-a334-7d2e-b9fa-b8fe5b44a6e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7e84-9777-7b4b8fd7b8a9" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_019dac15-a334-7d2e-b9fa-b8fe5b44a6e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019dac15-a334-76cf-a75d-79393f49a402" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7e84-9777-7b4b8fd7b8a9" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019dac15-a334-76cf-a75d-79393f49a402" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019dac15-a334-7485-811d-f9863284fc30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7e84-9777-7b4b8fd7b8a9" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019dac15-a334-7485-811d-f9863284fc30" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019dac15-a334-7a95-bc50-61b2a89f37a7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7e84-9777-7b4b8fd7b8a9" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019dac15-a334-7a95-bc50-61b2a89f37a7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityPeriodicPaymentPrincipal_019dac15-a334-74da-b563-d07928ca656a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityPeriodicPaymentPrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7e84-9777-7b4b8fd7b8a9" xlink:to="loc_us-gaap_LineOfCreditFacilityPeriodicPaymentPrincipal_019dac15-a334-74da-b563-d07928ca656a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019dac15-a334-7a1e-a315-89196a4568e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7e84-9777-7b4b8fd7b8a9" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019dac15-a334-7a1e-a315-89196a4568e3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_019dac15-a334-77f3-b724-21fbdce376e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7e84-9777-7b4b8fd7b8a9" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_019dac15-a334-77f3-b724-21fbdce376e4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentIssuedPrincipal_019dac15-a334-73ac-8ead-eca2059c7536" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentIssuedPrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7e84-9777-7b4b8fd7b8a9" xlink:to="loc_us-gaap_DebtInstrumentIssuedPrincipal_019dac15-a334-73ac-8ead-eca2059c7536" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentPeriodicPaymentPrincipal_019dac15-a334-735b-a07f-94513d541524" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentPeriodicPaymentPrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7e84-9777-7b4b8fd7b8a9" xlink:to="loc_us-gaap_DebtInstrumentPeriodicPaymentPrincipal_019dac15-a334-735b-a07f-94513d541524" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDebtNetOfIssuanceCosts_019dac15-a334-7407-9802-cdc3c8e4dcbd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromDebtNetOfIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7e84-9777-7b4b8fd7b8a9" xlink:to="loc_us-gaap_ProceedsFromDebtNetOfIssuanceCosts_019dac15-a334-7407-9802-cdc3c8e4dcbd" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019de46f-e24a-72e5-953f-936ee7e469ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7e84-9777-7b4b8fd7b8a9" xlink:to="loc_us-gaap_LineOfCredit_019de46f-e24a-72e5-953f-936ee7e469ab" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsGross_019de478-613c-7bab-a1e0-b27ce08ba8fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredFinanceCostsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7e84-9777-7b4b8fd7b8a9" xlink:to="loc_us-gaap_DeferredFinanceCostsGross_019de478-613c-7bab-a1e0-b27ce08ba8fe" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_LineOfCreditFacilityAbilityToExpandMaximumBorrowingCapacity_019de47a-b316-765f-af6e-d6d81a7f21e3" xlink:href="optu-20260331.xsd#optu_LineOfCreditFacilityAbilityToExpandMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7e84-9777-7b4b8fd7b8a9" xlink:to="loc_optu_LineOfCreditFacilityAbilityToExpandMaximumBorrowingCapacity_019de47a-b316-765f-af6e-d6d81a7f21e3" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/DEBTSummaryofDebtMaturitiesDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#DEBTSummaryofDebtMaturitiesDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/DEBTSummaryofDebtMaturitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7968-97cd-d2e91f236474" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7d97-930d-23a0d8604820" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7968-97cd-d2e91f236474" xlink:to="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7d97-930d-23a0d8604820" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-7401-8344-620cbcd73597" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7d97-930d-23a0d8604820" xlink:to="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-7401-8344-620cbcd73597" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7401-8344-620cbcd73597_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-7401-8344-620cbcd73597" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7401-8344-620cbcd73597_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7955-b97f-99284fa14bd9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-7401-8344-620cbcd73597" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7955-b97f-99284fa14bd9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_IncrementalTermLoanB6Member_019dac15-a334-7db0-a60a-a3d3368e376b" xlink:href="optu-20260331.xsd#optu_IncrementalTermLoanB6Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7955-b97f-99284fa14bd9" xlink:to="loc_optu_IncrementalTermLoanB6Member_019dac15-a334-7db0-a60a-a3d3368e376b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019dac15-a334-7023-8d95-c5fcbe65a0d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dac15-a334-7d97-930d-23a0d8604820" xlink:to="loc_us-gaap_CreditFacilityAxis_019dac15-a334-7023-8d95-c5fcbe65a0d5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019dac15-a334-7023-8d95-c5fcbe65a0d5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019dac15-a334-7023-8d95-c5fcbe65a0d5" xlink:to="loc_us-gaap_CreditFacilityDomain_019dac15-a334-7023-8d95-c5fcbe65a0d5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019dac15-a334-7a9c-958d-3990a50c3c22" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019dac15-a334-7023-8d95-c5fcbe65a0d5" xlink:to="loc_us-gaap_CreditFacilityDomain_019dac15-a334-7a9c-958d-3990a50c3c22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019dac15-a334-723c-bc1a-e037cd202950" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019dac15-a334-7a9c-958d-3990a50c3c22" xlink:to="loc_us-gaap_SecuredDebtMember_019dac15-a334-723c-bc1a-e037cd202950" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextRollingTwelveMonths_019dac15-a334-7a3d-bd7e-799327336066" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextRollingTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7968-97cd-d2e91f236474" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextRollingTwelveMonths_019dac15-a334-7a3d-bd7e-799327336066" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearTwo_019dac15-a334-7fb7-a0d2-ff97c41a5292" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7968-97cd-d2e91f236474" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearTwo_019dac15-a334-7fb7-a0d2-ff97c41a5292" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearThree_019dac15-a334-7194-a2e2-1394af565bc1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7968-97cd-d2e91f236474" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearThree_019dac15-a334-7194-a2e2-1394af565bc1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearFour_019dac15-a334-7a95-9aba-49cd08a013fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7968-97cd-d2e91f236474" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearFour_019dac15-a334-7a95-9aba-49cd08a013fd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearFive_019dac15-a334-75ba-94ed-4af4d2960eea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7968-97cd-d2e91f236474" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearFive_019dac15-a334-75ba-94ed-4af4d2960eea" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive_019dac15-a334-7067-80b1-cf44310885d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dac15-a334-7968-97cd-d2e91f236474" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive_019dac15-a334-7067-80b1-cf44310885d8" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/FAIRVALUEMEASUREMENTAssetsandLiabilitiesMeasuredatFairValueonaRecurringBasisDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#FAIRVALUEMEASUREMENTAssetsandLiabilitiesMeasuredatFairValueonaRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/FAIRVALUEMEASUREMENTAssetsandLiabilitiesMeasuredatFairValueonaRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7274-9d8a-329c4a1ddf88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7274-9d8a-329c4a1ddf88" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019dac15-a334-7862-9168-756d045c7815" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019dac15-a334-7862-9168-756d045c7815" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019dac15-a334-7862-9168-756d045c7815_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019dac15-a334-7862-9168-756d045c7815" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019dac15-a334-7862-9168-756d045c7815_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019dac15-a334-7b42-90d3-6a7c217d6897" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019dac15-a334-7862-9168-756d045c7815" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019dac15-a334-7b42-90d3-6a7c217d6897" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_019dac15-a334-7afc-bf12-fd52f4907652" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_019dac15-a334-7b42-90d3-6a7c217d6897" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_019dac15-a334-7afc-bf12-fd52f4907652" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dac15-a334-7b95-9dfe-55fd03e9ad70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dac15-a334-7b95-9dfe-55fd03e9ad70" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7b95-9dfe-55fd03e9ad70_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dac15-a334-7b95-9dfe-55fd03e9ad70" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7b95-9dfe-55fd03e9ad70_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7d02-8bf6-dc5404e31a90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dac15-a334-7b95-9dfe-55fd03e9ad70" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7d02-8bf6-dc5404e31a90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019dac15-a334-79e4-95c6-a64df36cd638" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7d02-8bf6-dc5404e31a90" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019dac15-a334-79e4-95c6-a64df36cd638" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019dac15-a334-7c59-a32b-4b25321c0112" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7d02-8bf6-dc5404e31a90" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019dac15-a334-7c59-a32b-4b25321c0112" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019dac15-a334-747b-a035-dcf6f3ba7b88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7d02-8bf6-dc5404e31a90" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019dac15-a334-747b-a035-dcf6f3ba7b88" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_019dac15-a334-7ef0-9540-beb6ac5d8fec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_019dac15-a334-7ef0-9540-beb6ac5d8fec" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019dac15-a334-7ef0-9540-beb6ac5d8fec_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019dac15-a334-7ef0-9540-beb6ac5d8fec" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019dac15-a334-7ef0-9540-beb6ac5d8fec_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019dac15-a334-7eb3-8e3b-1860f844d68a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019dac15-a334-7ef0-9540-beb6ac5d8fec" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019dac15-a334-7eb3-8e3b-1860f844d68a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019dac15-a334-7b6b-9953-2bbb5f696186" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019dac15-a334-7eb3-8e3b-1860f844d68a" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019dac15-a334-7b6b-9953-2bbb5f696186" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019dac15-a334-7f68-9147-95a83e9f1b31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019dac15-a334-7f68-9147-95a83e9f1b31" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dac15-a334-7f68-9147-95a83e9f1b31_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dac15-a334-7f68-9147-95a83e9f1b31" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dac15-a334-7f68-9147-95a83e9f1b31_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dac15-a334-7b13-b7ac-caf6a722bd2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dac15-a334-7f68-9147-95a83e9f1b31" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dac15-a334-7b13-b7ac-caf6a722bd2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019dac15-a334-7bcd-9fa5-6df03201d255" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019dac15-a334-7b13-b7ac-caf6a722bd2e" xlink:to="loc_us-gaap_InterestRateSwapMember_019dac15-a334-7bcd-9fa5-6df03201d255" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a334-78e8-a585-2088764791c4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_dei_LegalEntityAxis_019dac15-a334-78e8-a585-2088764791c4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a334-78e8-a585-2088764791c4_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a334-78e8-a585-2088764791c4" xlink:to="loc_dei_EntityDomain_019dac15-a334-78e8-a585-2088764791c4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a334-70be-a499-644e88d7da5a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a334-78e8-a585-2088764791c4" xlink:to="loc_dei_EntityDomain_019dac15-a334-70be-a499-644e88d7da5a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsMember_019dac15-a334-76c1-9079-2f437f7fce87" xlink:href="optu-20260331.xsd#optu_CSCHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a334-70be-a499-644e88d7da5a" xlink:to="loc_optu_CSCHoldingsMember_019dac15-a334-76c1-9079-2f437f7fce87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-703e-884d-863933d4e921" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-703e-884d-863933d4e921" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a334-703e-884d-863933d4e921_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-703e-884d-863933d4e921" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a334-703e-884d-863933d4e921_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a334-7cf6-a8fd-fff9bcf9bd11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-703e-884d-863933d4e921" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a334-7cf6-a8fd-fff9bcf9bd11" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dac15-a334-7f20-9768-60de1684d3b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019dac15-a334-7cf6-a8fd-fff9bcf9bd11" xlink:to="loc_us-gaap_RelatedPartyMember_019dac15-a334-7f20-9768-60de1684d3b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-7af7-9d9a-ed1dfa756f49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-7af7-9d9a-ed1dfa756f49" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-7af7-9d9a-ed1dfa756f49_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-7af7-9d9a-ed1dfa756f49" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-7af7-9d9a-ed1dfa756f49_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-79e9-9730-c7815978de0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-7af7-9d9a-ed1dfa756f49" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-79e9-9730-c7815978de0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableOtherPayablesMember_019dac15-a334-7058-a3d7-75cbc0128230" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayableOtherPayablesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-79e9-9730-c7815978de0c" xlink:to="loc_us-gaap_NotesPayableOtherPayablesMember_019dac15-a334-7058-a3d7-75cbc0128230" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeAxis_019dac15-a334-767e-96ac-550ed66b8991" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_us-gaap_ShortTermDebtTypeAxis_019dac15-a334-767e-96ac-550ed66b8991" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-767e-96ac-550ed66b8991_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_019dac15-a334-767e-96ac-550ed66b8991" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-767e-96ac-550ed66b8991_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-7002-88dc-1e2e5e5be3ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_019dac15-a334-767e-96ac-550ed66b8991" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-7002-88dc-1e2e5e5be3ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableOtherPayablesMember_019dac15-a334-7810-9b19-4fd0f39aa0a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayableOtherPayablesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-7002-88dc-1e2e5e5be3ce" xlink:to="loc_us-gaap_NotesPayableOtherPayablesMember_019dac15-a334-7810-9b19-4fd0f39aa0a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019dac15-a334-7137-9ff3-eedfd74ab6c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfFinancialPositionLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019dac15-a334-7137-9ff3-eedfd74ab6c1" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019dac15-a334-76fd-bfb2-6fcb6945faf3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_us-gaap_HedgingDesignationAxis_019dac15-a334-76fd-bfb2-6fcb6945faf3" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019dac15-a334-76fd-bfb2-6fcb6945faf3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019dac15-a334-76fd-bfb2-6fcb6945faf3" xlink:to="loc_us-gaap_HedgingDesignationDomain_019dac15-a334-76fd-bfb2-6fcb6945faf3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019dac15-a334-77ee-b87f-5f9c000ba3ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019dac15-a334-76fd-bfb2-6fcb6945faf3" xlink:to="loc_us-gaap_HedgingDesignationDomain_019dac15-a334-77ee-b87f-5f9c000ba3ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019dac15-a334-7cbd-b570-dd722328dd66" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019dac15-a334-77ee-b87f-5f9c000ba3ef" xlink:to="loc_us-gaap_NondesignatedMember_019dac15-a334-7cbd-b570-dd722328dd66" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_019dac15-a334-7224-9738-201f7095c449" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7274-9d8a-329c4a1ddf88" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_019dac15-a334-7224-9738-201f7095c449" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019dac15-a334-754b-87ac-b1e5f2293798" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019dac15-a334-7224-9738-201f7095c449" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019dac15-a334-754b-87ac-b1e5f2293798" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019dac15-a334-75e5-b62e-c221ebc76a28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7274-9d8a-329c4a1ddf88" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019dac15-a334-75e5-b62e-c221ebc76a28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_019dac15-a334-78ed-8df4-e39f78a1fa50" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019dac15-a334-75e5-b62e-c221ebc76a28" xlink:to="loc_us-gaap_DerivativeLiabilities_019dac15-a334-78ed-8df4-e39f78a1fa50" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019dac15-a334-76a7-806c-e00740ec7ffa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019dac15-a334-75e5-b62e-c221ebc76a28" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019dac15-a334-76a7-806c-e00740ec7ffa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayable_019dac15-a334-7450-9b3c-ba98f704e001" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7274-9d8a-329c4a1ddf88" xlink:to="loc_us-gaap_NotesPayable_019dac15-a334-7450-9b3c-ba98f704e001" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFairValue_019dac15-a334-710d-a3bd-02c25fecd49b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7274-9d8a-329c4a1ddf88" xlink:to="loc_us-gaap_DebtInstrumentFairValue_019dac15-a334-710d-a3bd-02c25fecd49b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_019dac15-a334-785f-b9f6-d18d94cfd306" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7274-9d8a-329c4a1ddf88" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_019dac15-a334-785f-b9f6-d18d94cfd306" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/FAIRVALUEMEASUREMENTAssetsandLiabilitiesMeasuredatFairValueonaRecurringBasisDetails_1" xlink:type="simple" xlink:href="optu-20260331.xsd#FAIRVALUEMEASUREMENTAssetsandLiabilitiesMeasuredatFairValueonaRecurringBasisDetails_1"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/FAIRVALUEMEASUREMENTAssetsandLiabilitiesMeasuredatFairValueonaRecurringBasisDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7274-9d8a-329c4a1ddf88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7274-9d8a-329c4a1ddf88" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019dac15-a334-7862-9168-756d045c7815" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019dac15-a334-7862-9168-756d045c7815" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019dac15-a334-7862-9168-756d045c7815_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019dac15-a334-7862-9168-756d045c7815" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019dac15-a334-7862-9168-756d045c7815_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019dac15-a334-7b42-90d3-6a7c217d6897" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019dac15-a334-7862-9168-756d045c7815" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019dac15-a334-7b42-90d3-6a7c217d6897" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_019dac15-a334-7afc-bf12-fd52f4907652" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_019dac15-a334-7b42-90d3-6a7c217d6897" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_019dac15-a334-7afc-bf12-fd52f4907652" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dac15-a334-7b95-9dfe-55fd03e9ad70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dac15-a334-7b95-9dfe-55fd03e9ad70" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7b95-9dfe-55fd03e9ad70_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dac15-a334-7b95-9dfe-55fd03e9ad70" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7b95-9dfe-55fd03e9ad70_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7d02-8bf6-dc5404e31a90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dac15-a334-7b95-9dfe-55fd03e9ad70" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7d02-8bf6-dc5404e31a90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019dac15-a334-79e4-95c6-a64df36cd638" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7d02-8bf6-dc5404e31a90" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019dac15-a334-79e4-95c6-a64df36cd638" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019dac15-a334-7c59-a32b-4b25321c0112" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7d02-8bf6-dc5404e31a90" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019dac15-a334-7c59-a32b-4b25321c0112" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019dac15-a334-747b-a035-dcf6f3ba7b88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7d02-8bf6-dc5404e31a90" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019dac15-a334-747b-a035-dcf6f3ba7b88" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_019dac15-a334-7ef0-9540-beb6ac5d8fec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_019dac15-a334-7ef0-9540-beb6ac5d8fec" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019dac15-a334-7ef0-9540-beb6ac5d8fec_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019dac15-a334-7ef0-9540-beb6ac5d8fec" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019dac15-a334-7ef0-9540-beb6ac5d8fec_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019dac15-a334-7eb3-8e3b-1860f844d68a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019dac15-a334-7ef0-9540-beb6ac5d8fec" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019dac15-a334-7eb3-8e3b-1860f844d68a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019dac15-a334-7b6b-9953-2bbb5f696186" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019dac15-a334-7eb3-8e3b-1860f844d68a" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019dac15-a334-7b6b-9953-2bbb5f696186" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019dac15-a334-7f68-9147-95a83e9f1b31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019dac15-a334-7f68-9147-95a83e9f1b31" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dac15-a334-7f68-9147-95a83e9f1b31_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dac15-a334-7f68-9147-95a83e9f1b31" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dac15-a334-7f68-9147-95a83e9f1b31_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dac15-a334-7b13-b7ac-caf6a722bd2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dac15-a334-7f68-9147-95a83e9f1b31" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dac15-a334-7b13-b7ac-caf6a722bd2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019dac15-a334-7bcd-9fa5-6df03201d255" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019dac15-a334-7b13-b7ac-caf6a722bd2e" xlink:to="loc_us-gaap_InterestRateSwapMember_019dac15-a334-7bcd-9fa5-6df03201d255" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a334-78e8-a585-2088764791c4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_dei_LegalEntityAxis_019dac15-a334-78e8-a585-2088764791c4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a334-78e8-a585-2088764791c4_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a334-78e8-a585-2088764791c4" xlink:to="loc_dei_EntityDomain_019dac15-a334-78e8-a585-2088764791c4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a334-70be-a499-644e88d7da5a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a334-78e8-a585-2088764791c4" xlink:to="loc_dei_EntityDomain_019dac15-a334-70be-a499-644e88d7da5a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsMember_019dac15-a334-76c1-9079-2f437f7fce87" xlink:href="optu-20260331.xsd#optu_CSCHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a334-70be-a499-644e88d7da5a" xlink:to="loc_optu_CSCHoldingsMember_019dac15-a334-76c1-9079-2f437f7fce87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-703e-884d-863933d4e921" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-703e-884d-863933d4e921" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a334-703e-884d-863933d4e921_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-703e-884d-863933d4e921" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a334-703e-884d-863933d4e921_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a334-7cf6-a8fd-fff9bcf9bd11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-703e-884d-863933d4e921" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a334-7cf6-a8fd-fff9bcf9bd11" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dac15-a334-7f20-9768-60de1684d3b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019dac15-a334-7cf6-a8fd-fff9bcf9bd11" xlink:to="loc_us-gaap_RelatedPartyMember_019dac15-a334-7f20-9768-60de1684d3b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-7af7-9d9a-ed1dfa756f49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-7af7-9d9a-ed1dfa756f49" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-7af7-9d9a-ed1dfa756f49_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-7af7-9d9a-ed1dfa756f49" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-7af7-9d9a-ed1dfa756f49_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-79e9-9730-c7815978de0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-7af7-9d9a-ed1dfa756f49" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-79e9-9730-c7815978de0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableOtherPayablesMember_019dac15-a334-7058-a3d7-75cbc0128230" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayableOtherPayablesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-79e9-9730-c7815978de0c" xlink:to="loc_us-gaap_NotesPayableOtherPayablesMember_019dac15-a334-7058-a3d7-75cbc0128230" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeAxis_019dac15-a334-767e-96ac-550ed66b8991" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_us-gaap_ShortTermDebtTypeAxis_019dac15-a334-767e-96ac-550ed66b8991" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-767e-96ac-550ed66b8991_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_019dac15-a334-767e-96ac-550ed66b8991" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-767e-96ac-550ed66b8991_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-7002-88dc-1e2e5e5be3ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_019dac15-a334-767e-96ac-550ed66b8991" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-7002-88dc-1e2e5e5be3ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableOtherPayablesMember_019dac15-a334-7810-9b19-4fd0f39aa0a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayableOtherPayablesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_019dac15-a334-7002-88dc-1e2e5e5be3ce" xlink:to="loc_us-gaap_NotesPayableOtherPayablesMember_019dac15-a334-7810-9b19-4fd0f39aa0a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019dac15-a334-76fd-bfb2-6fcb6945faf3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-711e-8c32-7376708f7004" xlink:to="loc_us-gaap_HedgingDesignationAxis_019dac15-a334-76fd-bfb2-6fcb6945faf3" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019dac15-a334-76fd-bfb2-6fcb6945faf3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019dac15-a334-76fd-bfb2-6fcb6945faf3" xlink:to="loc_us-gaap_HedgingDesignationDomain_019dac15-a334-76fd-bfb2-6fcb6945faf3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019dac15-a334-77ee-b87f-5f9c000ba3ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019dac15-a334-76fd-bfb2-6fcb6945faf3" xlink:to="loc_us-gaap_HedgingDesignationDomain_019dac15-a334-77ee-b87f-5f9c000ba3ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019dac15-a334-7cbd-b570-dd722328dd66" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019dac15-a334-77ee-b87f-5f9c000ba3ef" xlink:to="loc_us-gaap_NondesignatedMember_019dac15-a334-7cbd-b570-dd722328dd66" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_019dac15-a334-7224-9738-201f7095c449" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7274-9d8a-329c4a1ddf88" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_019dac15-a334-7224-9738-201f7095c449" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019dac15-a334-754b-87ac-b1e5f2293798" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019dac15-a334-7224-9738-201f7095c449" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019dac15-a334-754b-87ac-b1e5f2293798" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019dac15-a334-75e5-b62e-c221ebc76a28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7274-9d8a-329c4a1ddf88" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019dac15-a334-75e5-b62e-c221ebc76a28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_019dac15-a334-78ed-8df4-e39f78a1fa50" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019dac15-a334-75e5-b62e-c221ebc76a28" xlink:to="loc_us-gaap_DerivativeLiabilities_019dac15-a334-78ed-8df4-e39f78a1fa50" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019dac15-a334-76a7-806c-e00740ec7ffa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019dac15-a334-75e5-b62e-c221ebc76a28" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019dac15-a334-76a7-806c-e00740ec7ffa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayable_019dac15-a334-7450-9b3c-ba98f704e001" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7274-9d8a-329c4a1ddf88" xlink:to="loc_us-gaap_NotesPayable_019dac15-a334-7450-9b3c-ba98f704e001" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFairValue_019dac15-a334-710d-a3bd-02c25fecd49b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7274-9d8a-329c4a1ddf88" xlink:to="loc_us-gaap_DebtInstrumentFairValue_019dac15-a334-710d-a3bd-02c25fecd49b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_019dac15-a334-785f-b9f6-d18d94cfd306" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7274-9d8a-329c4a1ddf88" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_019dac15-a334-785f-b9f6-d18d94cfd306" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/FAIRVALUEMEASUREMENTCarryingValuesandEstimatedFairValuesofDebtInstrumentsDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#FAIRVALUEMEASUREMENTCarryingValuesandEstimatedFairValuesofDebtInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/FAIRVALUEMEASUREMENTCarryingValuesandEstimatedFairValuesofDebtInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7ced-9e70-0b81377f61fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-7280-9ea6-a2ef272fe499" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7ced-9e70-0b81377f61fb" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-7280-9ea6-a2ef272fe499" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019dac15-a334-78a8-b221-4dc85bb3c927" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-7280-9ea6-a2ef272fe499" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019dac15-a334-78a8-b221-4dc85bb3c927" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dac15-a334-78a8-b221-4dc85bb3c927_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019dac15-a334-78a8-b221-4dc85bb3c927" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dac15-a334-78a8-b221-4dc85bb3c927_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dac15-a334-7c41-9ac2-20c2637f3766" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019dac15-a334-78a8-b221-4dc85bb3c927" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dac15-a334-7c41-9ac2-20c2637f3766" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dac15-a334-77bb-accc-4f8708c939b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dac15-a334-7c41-9ac2-20c2637f3766" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dac15-a334-77bb-accc-4f8708c939b7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019dac15-a334-71ed-b142-a1429543bd6d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dac15-a334-77bb-accc-4f8708c939b7" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019dac15-a334-71ed-b142-a1429543bd6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019dac15-a334-75ce-be52-df2f1c6babe4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dac15-a334-77bb-accc-4f8708c939b7" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019dac15-a334-75ce-be52-df2f1c6babe4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dac15-a334-75b1-bc00-8ac9b481f8d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-7280-9ea6-a2ef272fe499" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dac15-a334-75b1-bc00-8ac9b481f8d7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-75b1-bc00-8ac9b481f8d7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dac15-a334-75b1-bc00-8ac9b481f8d7" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-75b1-bc00-8ac9b481f8d7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7f2f-bec0-121bb786076c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dac15-a334-75b1-bc00-8ac9b481f8d7" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7f2f-bec0-121bb786076c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019dac15-a334-7a1d-bcaf-d126c8558c54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7f2f-bec0-121bb786076c" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019dac15-a334-7a1d-bcaf-d126c8558c54" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019dac15-a334-7798-bcd6-fa3bddf26dc2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7f2f-bec0-121bb786076c" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019dac15-a334-7798-bcd6-fa3bddf26dc2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019dac15-a334-7b55-a62b-ebecc634d302" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dac15-a334-7f2f-bec0-121bb786076c" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019dac15-a334-7b55-a62b-ebecc634d302" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a334-7643-b614-2c0d1c697d0c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-7280-9ea6-a2ef272fe499" xlink:to="loc_dei_LegalEntityAxis_019dac15-a334-7643-b614-2c0d1c697d0c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a334-7643-b614-2c0d1c697d0c_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a334-7643-b614-2c0d1c697d0c" xlink:to="loc_dei_EntityDomain_019dac15-a334-7643-b614-2c0d1c697d0c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a334-744e-8e79-e8e604690be8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a334-7643-b614-2c0d1c697d0c" xlink:to="loc_dei_EntityDomain_019dac15-a334-744e-8e79-e8e604690be8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsMember_019dac15-a334-778e-9ec7-1e6a6fcf5b36" xlink:href="optu-20260331.xsd#optu_CSCHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a334-744e-8e79-e8e604690be8" xlink:to="loc_optu_CSCHoldingsMember_019dac15-a334-778e-9ec7-1e6a6fcf5b36" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_UnSubGroupMember_019de3c8-39d1-7762-b2e1-70e229832707" xlink:href="optu-20260331.xsd#optu_UnSubGroupMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a334-744e-8e79-e8e604690be8" xlink:to="loc_optu_UnSubGroupMember_019de3c8-39d1-7762-b2e1-70e229832707" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CablevisionLightpathMember_019de3cc-3b83-7e58-b731-e1e8b0b57cf8" xlink:href="optu-20260331.xsd#optu_CablevisionLightpathMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a334-744e-8e79-e8e604690be8" xlink:to="loc_optu_CablevisionLightpathMember_019de3cc-3b83-7e58-b731-e1e8b0b57cf8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-7eae-91ab-0f2a48e4dc52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-7280-9ea6-a2ef272fe499" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-7eae-91ab-0f2a48e4dc52" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-7eae-91ab-0f2a48e4dc52_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-7eae-91ab-0f2a48e4dc52" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-7eae-91ab-0f2a48e4dc52_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-7ff7-8516-c96b146259bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019dac15-a334-7eae-91ab-0f2a48e4dc52" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-7ff7-8516-c96b146259bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019dac15-a334-726c-8cc3-5a5ad94b4495" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-7ff7-8516-c96b146259bc" xlink:to="loc_us-gaap_LineOfCreditMember_019dac15-a334-726c-8cc3-5a5ad94b4495" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_SeniorGuaranteeNotesMember_019dac15-a334-7767-afa0-40bf4d57592c" xlink:href="optu-20260331.xsd#optu_SeniorGuaranteeNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-7ff7-8516-c96b146259bc" xlink:to="loc_optu_SeniorGuaranteeNotesMember_019dac15-a334-7767-afa0-40bf4d57592c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorDebtObligationsMember_019dac15-a334-711e-9815-970fcee877a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorDebtObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-7ff7-8516-c96b146259bc" xlink:to="loc_us-gaap_SeniorDebtObligationsMember_019dac15-a334-711e-9815-970fcee877a8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableOtherPayablesMember_019dac15-a334-745e-85b1-e99aa2204590" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayableOtherPayablesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-7ff7-8516-c96b146259bc" xlink:to="loc_us-gaap_NotesPayableOtherPayablesMember_019dac15-a334-745e-85b1-e99aa2204590" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_ReceivableFacilityLoanMember_019dac15-a334-77ee-8263-7d1f1272196d" xlink:href="optu-20260331.xsd#optu_ReceivableFacilityLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-7ff7-8516-c96b146259bc" xlink:to="loc_optu_ReceivableFacilityLoanMember_019dac15-a334-77ee-8263-7d1f1272196d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorSubordinatedNotesMember_019dac15-a334-797f-b3eb-c75cfed70c0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorSubordinatedNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-7ff7-8516-c96b146259bc" xlink:to="loc_us-gaap_SeniorSubordinatedNotesMember_019dac15-a334-797f-b3eb-c75cfed70c0d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_UnsubGroupCreditFacilityMember_019de3ca-020d-7ff6-a576-d7f62be76607" xlink:href="optu-20260331.xsd#optu_UnsubGroupCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-7ff7-8516-c96b146259bc" xlink:to="loc_optu_UnsubGroupCreditFacilityMember_019de3ca-020d-7ff6-a576-d7f62be76607" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_SecuredFiberNetworkRevenueNotesMember_019de3cc-a9ae-77a1-88ff-544c8871456b" xlink:href="optu-20260331.xsd#optu_SecuredFiberNetworkRevenueNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-7ff7-8516-c96b146259bc" xlink:to="loc_optu_SecuredFiberNetworkRevenueNotesMember_019de3cc-a9ae-77a1-88ff-544c8871456b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_NYCABSReceivableFacilityLoanMember_019de3ce-14dc-7119-b058-adc049794ccc" xlink:href="optu-20260331.xsd#optu_NYCABSReceivableFacilityLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dac15-a334-7ff7-8516-c96b146259bc" xlink:to="loc_optu_NYCABSReceivableFacilityLoanMember_019de3ce-14dc-7119-b058-adc049794ccc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_019dac15-a334-707b-9795-a1ef60751015" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-7280-9ea6-a2ef272fe499" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_019dac15-a334-707b-9795-a1ef60751015" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019dac15-a334-707b-9795-a1ef60751015_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019dac15-a334-707b-9795-a1ef60751015" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019dac15-a334-707b-9795-a1ef60751015_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019dac15-a334-7ff1-b1ca-d1d418684028" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019dac15-a334-707b-9795-a1ef60751015" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019dac15-a334-7ff1-b1ca-d1d418684028" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019dac15-a334-7ad6-a468-c36401c40001" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019dac15-a334-7ff1-b1ca-d1d418684028" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019dac15-a334-7ad6-a468-c36401c40001" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019dac15-a334-7798-a7de-c59f40d066a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-7280-9ea6-a2ef272fe499" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019dac15-a334-7798-a7de-c59f40d066a9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019dac15-a334-7798-a7de-c59f40d066a9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019dac15-a334-7798-a7de-c59f40d066a9" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019dac15-a334-7798-a7de-c59f40d066a9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019dac15-a334-7f6f-a501-e78db8727c2f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019dac15-a334-7798-a7de-c59f40d066a9" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019dac15-a334-7f6f-a501-e78db8727c2f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_019dac15-a334-7993-a14a-6689aad8808c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_019dac15-a334-7f6f-a501-e78db8727c2f" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_019dac15-a334-7993-a14a-6689aad8808c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-71b2-86bb-51c5c1bb4c27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-7280-9ea6-a2ef272fe499" xlink:to="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-71b2-86bb-51c5c1bb4c27" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-71b2-86bb-51c5c1bb4c27_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-71b2-86bb-51c5c1bb4c27" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-71b2-86bb-51c5c1bb4c27_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7b10-a569-e7c9c077fe34" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dac15-a334-71b2-86bb-51c5c1bb4c27" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7b10-a569-e7c9c077fe34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_ReceivableFacilityLoanMember_019dac15-a334-71f8-a0a0-4a428df7fea1" xlink:href="optu-20260331.xsd#optu_ReceivableFacilityLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dac15-a334-7b10-a569-e7c9c077fe34" xlink:to="loc_optu_ReceivableFacilityLoanMember_019dac15-a334-71f8-a0a0-4a428df7fea1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019de3ce-df5c-7794-8577-e0b637fa6121" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dac15-a334-7280-9ea6-a2ef272fe499" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019de3ce-df5c-7794-8577-e0b637fa6121" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019de3ce-df5c-7794-8577-e0b637fa6121_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019de3ce-df5c-7794-8577-e0b637fa6121" xlink:to="loc_us-gaap_RelatedPartyDomain_019de3ce-df5c-7794-8577-e0b637fa6121_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019de3ce-df5c-7d1c-92d5-20bb0b95773b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019de3ce-df5c-7794-8577-e0b637fa6121" xlink:to="loc_us-gaap_RelatedPartyDomain_019de3ce-df5c-7d1c-92d5-20bb0b95773b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019de3ce-df5c-77fb-b74e-4a8b1356c28c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019de3ce-df5c-7d1c-92d5-20bb0b95773b" xlink:to="loc_us-gaap_RelatedPartyMember_019de3ce-df5c-77fb-b74e-4a8b1356c28c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFairValue_019dac15-a334-753b-9840-f910e02056ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7ced-9e70-0b81377f61fb" xlink:to="loc_us-gaap_DebtInstrumentFairValue_019dac15-a334-753b-9840-f910e02056ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019dac15-a334-7a9b-b883-3b18feb6e523" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7ced-9e70-0b81377f61fb" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019dac15-a334-7a9b-b883-3b18feb6e523" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayable_019de3ce-df5c-7e4e-bdfa-cf364a3cc98d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dac15-a334-7ced-9e70-0b81377f61fb" xlink:to="loc_us-gaap_NotesPayable_019de3ce-df5c-7e4e-bdfa-cf364a3cc98d" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/INCOMETAXESIncomeTaxExpenseBenefitContinuingOperationsDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#INCOMETAXESIncomeTaxExpenseBenefitContinuingOperationsDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/INCOMETAXESIncomeTaxExpenseBenefitContinuingOperationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_optu_IncomeTaxLineItems_019dac15-a334-75f1-b96a-e5dd1960e8a3" xlink:href="optu-20260331.xsd#optu_IncomeTaxLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_IncomeTaxTable_019dac15-a334-7104-8a76-f4e168980c6e" xlink:href="optu-20260331.xsd#optu_IncomeTaxTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_optu_IncomeTaxLineItems_019dac15-a334-75f1-b96a-e5dd1960e8a3" xlink:to="loc_optu_IncomeTaxTable_019dac15-a334-7104-8a76-f4e168980c6e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a334-70c1-a4b2-1e7f04da7297" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_optu_IncomeTaxTable_019dac15-a334-7104-8a76-f4e168980c6e" xlink:to="loc_dei_LegalEntityAxis_019dac15-a334-70c1-a4b2-1e7f04da7297" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a334-70c1-a4b2-1e7f04da7297_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a334-70c1-a4b2-1e7f04da7297" xlink:to="loc_dei_EntityDomain_019dac15-a334-70c1-a4b2-1e7f04da7297_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a334-7cac-8c1e-9ef9e1697197" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a334-70c1-a4b2-1e7f04da7297" xlink:to="loc_dei_EntityDomain_019dac15-a334-7cac-8c1e-9ef9e1697197" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsMember_019dac15-a334-7da3-ad1a-26bd03203004" xlink:href="optu-20260331.xsd#optu_CSCHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a334-7cac-8c1e-9ef9e1697197" xlink:to="loc_optu_CSCHoldingsMember_019dac15-a334-7da3-ad1a-26bd03203004" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019dac15-a334-7f87-a1b5-62544d1c824d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_optu_IncomeTaxLineItems_019dac15-a334-75f1-b96a-e5dd1960e8a3" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019dac15-a334-7f87-a1b5-62544d1c824d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019dac15-a334-7c20-aa61-ddef5e55a3b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_optu_IncomeTaxLineItems_019dac15-a334-75f1-b96a-e5dd1960e8a3" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019dac15-a334-7c20-aa61-ddef5e55a3b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CurrentStateAndLocalTaxExpenseBenefit_019dac15-a334-73a8-94e0-9255450b454a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CurrentStateAndLocalTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_optu_IncomeTaxLineItems_019dac15-a334-75f1-b96a-e5dd1960e8a3" xlink:to="loc_us-gaap_CurrentStateAndLocalTaxExpenseBenefit_019dac15-a334-73a8-94e0-9255450b454a" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/SHAREBASEDCOMPENSATIONScheduleofShareBasedCompensationExpenseBenefitDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#SHAREBASEDCOMPENSATIONScheduleofShareBasedCompensationExpenseBenefitDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/SHAREBASEDCOMPENSATIONScheduleofShareBasedCompensationExpenseBenefitDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019dac15-a334-7721-bfa4-201ef63b123c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019dac15-a334-7422-b5fe-bc95a2bb93c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019dac15-a334-7721-bfa4-201ef63b123c" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019dac15-a334-7422-b5fe-bc95a2bb93c8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019dac15-a334-7bac-98ff-b916aad517d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019dac15-a334-7422-b5fe-bc95a2bb93c8" xlink:to="loc_us-gaap_AwardTypeAxis_019dac15-a334-7bac-98ff-b916aad517d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7bac-98ff-b916aad517d2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019dac15-a334-7bac-98ff-b916aad517d2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7bac-98ff-b916aad517d2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7050-9250-957135fd7d17" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019dac15-a334-7bac-98ff-b916aad517d2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7050-9250-957135fd7d17" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019dac15-a334-765e-a4c8-6d51ced43fb5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7050-9250-957135fd7d17" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019dac15-a334-765e-a4c8-6d51ced43fb5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019dac15-a334-7854-8ab6-ca79688e4198" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7050-9250-957135fd7d17" xlink:to="loc_us-gaap_PerformanceSharesMember_019dac15-a334-7854-8ab6-ca79688e4198" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019dac15-a334-7ba4-8598-2a1a4a319db1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7050-9250-957135fd7d17" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019dac15-a334-7ba4-8598-2a1a4a319db1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_DeferredCashDenominatedPerformanceAwardMember_019dac15-a334-79e8-a85d-af0068e01199" xlink:href="optu-20260331.xsd#optu_DeferredCashDenominatedPerformanceAwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7050-9250-957135fd7d17" xlink:to="loc_optu_DeferredCashDenominatedPerformanceAwardMember_019dac15-a334-79e8-a85d-af0068e01199" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_OtherAwardsMember_019dac15-a334-7487-b06d-4120ba66bcb5" xlink:href="optu-20260331.xsd#optu_OtherAwardsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7050-9250-957135fd7d17" xlink:to="loc_optu_OtherAwardsMember_019dac15-a334-7487-b06d-4120ba66bcb5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019dac15-a334-7b0c-8d2b-56ff22b1d3f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019dac15-a334-7422-b5fe-bc95a2bb93c8" xlink:to="loc_us-gaap_PlanNameAxis_019dac15-a334-7b0c-8d2b-56ff22b1d3f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019dac15-a334-7b0c-8d2b-56ff22b1d3f4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019dac15-a334-7b0c-8d2b-56ff22b1d3f4" xlink:to="loc_us-gaap_PlanNameDomain_019dac15-a334-7b0c-8d2b-56ff22b1d3f4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019dac15-a334-79c3-b107-6bc3b3b1e3f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019dac15-a334-7b0c-8d2b-56ff22b1d3f4" xlink:to="loc_us-gaap_PlanNameDomain_019dac15-a334-79c3-b107-6bc3b3b1e3f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_A2017LTIPMember_019dac15-a334-784e-ab22-3c1307dbcb8e" xlink:href="optu-20260331.xsd#optu_A2017LTIPMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019dac15-a334-79c3-b107-6bc3b3b1e3f9" xlink:to="loc_optu_A2017LTIPMember_019dac15-a334-784e-ab22-3c1307dbcb8e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_A2019LTIPMember_019dac15-a334-783c-9015-26c4f9aefaeb" xlink:href="optu-20260331.xsd#optu_A2019LTIPMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019dac15-a334-79c3-b107-6bc3b3b1e3f9" xlink:to="loc_optu_A2019LTIPMember_019dac15-a334-783c-9015-26c4f9aefaeb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019dac15-a334-7024-86f4-b85ee26db5b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019dac15-a334-7721-bfa4-201ef63b123c" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019dac15-a334-7024-86f4-b85ee26db5b7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_ShareBasedCompensationUnrecognizedDeferredCompensationCost_019dac15-a334-71a9-b963-96187a00565a" xlink:href="optu-20260331.xsd#optu_ShareBasedCompensationUnrecognizedDeferredCompensationCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019dac15-a334-7721-bfa4-201ef63b123c" xlink:to="loc_optu_ShareBasedCompensationUnrecognizedDeferredCompensationCost_019dac15-a334-71a9-b963-96187a00565a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_AmountOfDeferredCashPerformanceAwardsOutstanding_019dac15-a334-725f-b9e6-eb97930e6cc2" xlink:href="optu-20260331.xsd#optu_AmountOfDeferredCashPerformanceAwardsOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019dac15-a334-7721-bfa4-201ef63b123c" xlink:to="loc_optu_AmountOfDeferredCashPerformanceAwardsOutstanding_019dac15-a334-725f-b9e6-eb97930e6cc2" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/SHAREBASEDCOMPENSATIONPerformanceandRestrictedUnitAwardDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#SHAREBASEDCOMPENSATIONPerformanceandRestrictedUnitAwardDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/SHAREBASEDCOMPENSATIONPerformanceandRestrictedUnitAwardDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019dac15-a334-7f39-a5f5-2088051704af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019dac15-a334-7b23-85e2-00b2d26d3a0a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019dac15-a334-7f39-a5f5-2088051704af" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019dac15-a334-7b23-85e2-00b2d26d3a0a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019dac15-a334-75ff-96f1-b20d4f826b32" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019dac15-a334-7b23-85e2-00b2d26d3a0a" xlink:to="loc_us-gaap_PlanNameAxis_019dac15-a334-75ff-96f1-b20d4f826b32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019dac15-a334-75ff-96f1-b20d4f826b32_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019dac15-a334-75ff-96f1-b20d4f826b32" xlink:to="loc_us-gaap_PlanNameDomain_019dac15-a334-75ff-96f1-b20d4f826b32_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019dac15-a334-7c6b-b661-a2ab0cbd5a80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019dac15-a334-75ff-96f1-b20d4f826b32" xlink:to="loc_us-gaap_PlanNameDomain_019dac15-a334-7c6b-b661-a2ab0cbd5a80" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_A2017LTIPMember_019dac15-a334-79da-9f35-38b4de83a7b0" xlink:href="optu-20260331.xsd#optu_A2017LTIPMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019dac15-a334-7c6b-b661-a2ab0cbd5a80" xlink:to="loc_optu_A2017LTIPMember_019dac15-a334-79da-9f35-38b4de83a7b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019dac15-a334-739b-9bc5-976c620446c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019dac15-a334-7b23-85e2-00b2d26d3a0a" xlink:to="loc_us-gaap_AwardTypeAxis_019dac15-a334-739b-9bc5-976c620446c3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-739b-9bc5-976c620446c3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019dac15-a334-739b-9bc5-976c620446c3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-739b-9bc5-976c620446c3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7b54-95df-edb4f35a22d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019dac15-a334-739b-9bc5-976c620446c3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7b54-95df-edb4f35a22d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019dac15-a334-73ae-b759-a61600b6f0cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7b54-95df-edb4f35a22d1" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019dac15-a334-73ae-b759-a61600b6f0cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_DeferredCashDenominatedPerformanceAwardMember_019dac15-a334-7423-97a0-c99ff190436c" xlink:href="optu-20260331.xsd#optu_DeferredCashDenominatedPerformanceAwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7b54-95df-edb4f35a22d1" xlink:to="loc_optu_DeferredCashDenominatedPerformanceAwardMember_019dac15-a334-7423-97a0-c99ff190436c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019dac15-a334-7294-8415-793d719cb1be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019dac15-a334-7f39-a5f5-2088051704af" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019dac15-a334-7294-8415-793d719cb1be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_019dac15-a334-7574-9854-5ed4bf6da479" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019dac15-a334-7294-8415-793d719cb1be" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_019dac15-a334-7574-9854-5ed4bf6da479" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_019dac15-a334-78b0-8bd3-5d7b83550b78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019dac15-a334-7294-8415-793d719cb1be" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_019dac15-a334-78b0-8bd3-5d7b83550b78" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019dac15-a334-76d3-b9c7-fcaece74ce47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019dac15-a334-7294-8415-793d719cb1be" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019dac15-a334-76d3-b9c7-fcaece74ce47" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_019dac15-a334-71be-b161-04c5f1dd5aae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019dac15-a334-7294-8415-793d719cb1be" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_019dac15-a334-71be-b161-04c5f1dd5aae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_019dac15-a334-7a52-80aa-60cb7c5b3dfe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/SHAREBASEDCOMPENSATIONNarrativeDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#SHAREBASEDCOMPENSATIONNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/SHAREBASEDCOMPENSATIONNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019dac15-a334-7db8-a06c-c7ca826c7139" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019dac15-a334-7b06-9809-c2d92d99c6e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019dac15-a334-7db8-a06c-c7ca826c7139" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019dac15-a334-7b06-9809-c2d92d99c6e2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019dac15-a334-7e18-8414-17d0e0f0580e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019dac15-a334-7b06-9809-c2d92d99c6e2" xlink:to="loc_srt_RangeAxis_019dac15-a334-7e18-8414-17d0e0f0580e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019dac15-a334-7e18-8414-17d0e0f0580e_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019dac15-a334-7e18-8414-17d0e0f0580e" xlink:to="loc_srt_RangeMember_019dac15-a334-7e18-8414-17d0e0f0580e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019dac15-a334-71de-904c-3700b81d26f3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019dac15-a334-7e18-8414-17d0e0f0580e" xlink:to="loc_srt_RangeMember_019dac15-a334-71de-904c-3700b81d26f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019dac15-a334-7f96-a6e1-8d9b2f0fa1ca" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019dac15-a334-71de-904c-3700b81d26f3" xlink:to="loc_srt_MaximumMember_019dac15-a334-7f96-a6e1-8d9b2f0fa1ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019dac15-a334-7ab9-be95-89a09724a8ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019dac15-a334-7b06-9809-c2d92d99c6e2" xlink:to="loc_us-gaap_AwardTypeAxis_019dac15-a334-7ab9-be95-89a09724a8ba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7ab9-be95-89a09724a8ba_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019dac15-a334-7ab9-be95-89a09724a8ba" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7ab9-be95-89a09724a8ba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-76a2-b16b-0d5b7a47e28c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019dac15-a334-7ab9-be95-89a09724a8ba" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-76a2-b16b-0d5b7a47e28c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_ClassA1ManagementIncentiveUnitsMember_019dac15-a334-70c5-8736-cd3b8d8dc1ce" xlink:href="optu-20260331.xsd#optu_ClassA1ManagementIncentiveUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-76a2-b16b-0d5b7a47e28c" xlink:to="loc_optu_ClassA1ManagementIncentiveUnitsMember_019dac15-a334-70c5-8736-cd3b8d8dc1ce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_ClassA2ManagementIncentiveUnitsMember_019dac15-a334-741c-a96a-3889f1501f4e" xlink:href="optu-20260331.xsd#optu_ClassA2ManagementIncentiveUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-76a2-b16b-0d5b7a47e28c" xlink:to="loc_optu_ClassA2ManagementIncentiveUnitsMember_019dac15-a334-741c-a96a-3889f1501f4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019dac15-a334-7c55-811d-8d7eab7f5f44" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-76a2-b16b-0d5b7a47e28c" xlink:to="loc_us-gaap_PerformanceSharesMember_019dac15-a334-7c55-811d-8d7eab7f5f44" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019dac15-a334-785f-a724-7b3d83f03bd7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-76a2-b16b-0d5b7a47e28c" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019dac15-a334-785f-a724-7b3d83f03bd7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_DeferredCashDenominatedPerformanceAwardMember_019de45b-77f4-710d-bb82-94436747585d" xlink:href="optu-20260331.xsd#optu_DeferredCashDenominatedPerformanceAwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-76a2-b16b-0d5b7a47e28c" xlink:to="loc_optu_DeferredCashDenominatedPerformanceAwardMember_019de45b-77f4-710d-bb82-94436747585d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_DeferredCashDenominatedAwardMember_019de45c-cf64-78e3-89d4-439aae208dc6" xlink:href="optu-20260331.xsd#optu_DeferredCashDenominatedAwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-76a2-b16b-0d5b7a47e28c" xlink:to="loc_optu_DeferredCashDenominatedAwardMember_019de45c-cf64-78e3-89d4-439aae208dc6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019dac15-a334-7ce3-90b6-8a07bc33ba44" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019dac15-a334-7b06-9809-c2d92d99c6e2" xlink:to="loc_us-gaap_PlanNameAxis_019dac15-a334-7ce3-90b6-8a07bc33ba44" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019dac15-a334-7ce3-90b6-8a07bc33ba44_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019dac15-a334-7ce3-90b6-8a07bc33ba44" xlink:to="loc_us-gaap_PlanNameDomain_019dac15-a334-7ce3-90b6-8a07bc33ba44_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019dac15-a334-7c58-afdf-138988751f81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019dac15-a334-7ce3-90b6-8a07bc33ba44" xlink:to="loc_us-gaap_PlanNameDomain_019dac15-a334-7c58-afdf-138988751f81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_A2021LightpathIncentivePlanMember_019dac15-a334-7968-83e9-5c758d0fbb47" xlink:href="optu-20260331.xsd#optu_A2021LightpathIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019dac15-a334-7c58-afdf-138988751f81" xlink:to="loc_optu_A2021LightpathIncentivePlanMember_019dac15-a334-7968-83e9-5c758d0fbb47" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_A2017LTIPMember_019dac15-a334-7f76-8c97-3628bd45cfd6" xlink:href="optu-20260331.xsd#optu_A2017LTIPMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019dac15-a334-7c58-afdf-138988751f81" xlink:to="loc_optu_A2017LTIPMember_019dac15-a334-7f76-8c97-3628bd45cfd6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_A2017LTIP3YearAwardMember_019dac15-a334-7667-aca1-9f0f70704ae6" xlink:href="optu-20260331.xsd#optu_A2017LTIP3YearAwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019dac15-a334-7c58-afdf-138988751f81" xlink:to="loc_optu_A2017LTIP3YearAwardMember_019dac15-a334-7667-aca1-9f0f70704ae6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_A2017LTIP4YearAwardMember_019dac15-a334-7152-80ba-ed28535a4a91" xlink:href="optu-20260331.xsd#optu_A2017LTIP4YearAwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019dac15-a334-7c58-afdf-138988751f81" xlink:to="loc_optu_A2017LTIP4YearAwardMember_019dac15-a334-7152-80ba-ed28535a4a91" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_019dac15-a334-7790-8daa-d1641d5065c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019dac15-a334-7b06-9809-c2d92d99c6e2" xlink:to="loc_us-gaap_VestingAxis_019dac15-a334-7790-8daa-d1641d5065c9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019dac15-a334-7790-8daa-d1641d5065c9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_019dac15-a334-7790-8daa-d1641d5065c9" xlink:to="loc_us-gaap_VestingDomain_019dac15-a334-7790-8daa-d1641d5065c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019dac15-a334-7b9b-89bc-4aa9f6c64939" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_019dac15-a334-7790-8daa-d1641d5065c9" xlink:to="loc_us-gaap_VestingDomain_019dac15-a334-7b9b-89bc-4aa9f6c64939" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_019dac15-a334-76ab-8a3a-99c08141d1e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019dac15-a334-7b9b-89bc-4aa9f6c64939" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_019dac15-a334-76ab-8a3a-99c08141d1e6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_019dac15-a334-7aa4-a5a5-201d91993532" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019dac15-a334-7b9b-89bc-4aa9f6c64939" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_019dac15-a334-7aa4-a5a5-201d91993532" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_019dac15-a334-7a25-b664-756209429291" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019dac15-a334-7b9b-89bc-4aa9f6c64939" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_019dac15-a334-7a25-b664-756209429291" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_PayoutAmountBasedOnMeetingTargetValuesForDeferredCashPerformanceAwards_019dac15-a334-7864-8a04-94bf87350b4a" xlink:href="optu-20260331.xsd#optu_PayoutAmountBasedOnMeetingTargetValuesForDeferredCashPerformanceAwards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019dac15-a334-7db8-a06c-c7ca826c7139" xlink:to="loc_optu_PayoutAmountBasedOnMeetingTargetValuesForDeferredCashPerformanceAwards_019dac15-a334-7864-8a04-94bf87350b4a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019dac15-a334-7b45-af6d-010de113ec95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019dac15-a334-7db8-a06c-c7ca826c7139" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019dac15-a334-7b45-af6d-010de113ec95" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_GrantDateFairValueOfAwardUnits_019dac15-a334-79cf-900f-f0eb433f4627" xlink:href="optu-20260331.xsd#optu_GrantDateFairValueOfAwardUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019dac15-a334-7db8-a06c-c7ca826c7139" xlink:to="loc_optu_GrantDateFairValueOfAwardUnits_019dac15-a334-79cf-900f-f0eb433f4627" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_019dac15-a334-7973-bf49-5ecbb2318d80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019dac15-a334-7db8-a06c-c7ca826c7139" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_019dac15-a334-7973-bf49-5ecbb2318d80" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019dac15-a334-71b4-b721-316dba99c89d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019dac15-a334-7db8-a06c-c7ca826c7139" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019dac15-a334-71b4-b721-316dba99c89d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_019dac15-a334-7fc7-be47-cab2076ee49d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019dac15-a334-7db8-a06c-c7ca826c7139" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_019dac15-a334-7fc7-be47-cab2076ee49d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_019dac15-a334-7d99-a1c1-bf4ab8fa01b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019dac15-a334-7db8-a06c-c7ca826c7139" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_019dac15-a334-7d99-a1c1-bf4ab8fa01b7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019dac15-a334-7911-a9e9-27338f45e825" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019dac15-a334-7db8-a06c-c7ca826c7139" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019dac15-a334-7911-a9e9-27338f45e825" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_019dac15-a334-7f11-b1eb-6c26aa3e6eb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019dac15-a334-7db8-a06c-c7ca826c7139" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_019dac15-a334-7f11-b1eb-6c26aa3e6eb3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_019de45b-77f4-7e80-8e4e-3520c6ef4014" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019dac15-a334-7db8-a06c-c7ca826c7139" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_019de45b-77f4-7e80-8e4e-3520c6ef4014" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense_019de45f-101a-76e3-a228-1aa95c1dd1de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019dac15-a334-7db8-a06c-c7ca826c7139" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense_019de45f-101a-76e3-a228-1aa95c1dd1de" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/AFFILIATEANDRELATEDPARTYTRANSACTIONSRevenueandRelatedChargesDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#AFFILIATEANDRELATEDPARTYTRANSACTIONSRevenueandRelatedChargesDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/AFFILIATEANDRELATEDPARTYTRANSACTIONSRevenueandRelatedChargesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7d6b-a0b2-0ec1b59b01e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dac15-a334-75e9-a223-0261defeaa8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7d6b-a0b2-0ec1b59b01e2" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dac15-a334-75e9-a223-0261defeaa8e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-728e-853a-62e3913e9794" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dac15-a334-75e9-a223-0261defeaa8e" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-728e-853a-62e3913e9794" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a334-728e-853a-62e3913e9794_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-728e-853a-62e3913e9794" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a334-728e-853a-62e3913e9794_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a334-7e1e-b100-b3492faaeb6a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-728e-853a-62e3913e9794" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a334-7e1e-b100-b3492faaeb6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dac15-a334-7776-91fb-c28c81b1651d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019dac15-a334-7e1e-b100-b3492faaeb6a" xlink:to="loc_us-gaap_RelatedPartyMember_019dac15-a334-7776-91fb-c28c81b1651d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019dac15-a334-783f-950f-2e64bf2f72bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7d6b-a0b2-0ec1b59b01e2" xlink:to="loc_us-gaap_Revenues_019dac15-a334-783f-950f-2e64bf2f72bb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_019dac15-a334-717b-8e3e-ff89fbd6f9b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7d6b-a0b2-0ec1b59b01e2" xlink:to="loc_us-gaap_OperatingExpensesAbstract_019dac15-a334-717b-8e3e-ff89fbd6f9b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_019dac15-a334-7b2d-b7e1-da364cdb3b2f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019dac15-a334-717b-8e3e-ff89fbd6f9b3" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_019dac15-a334-7b2d-b7e1-da364cdb3b2f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCostAndExpenseOperating_019dac15-a334-7adc-95a2-a4624b545779" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCostAndExpenseOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019dac15-a334-717b-8e3e-ff89fbd6f9b3" xlink:to="loc_us-gaap_OtherCostAndExpenseOperating_019dac15-a334-7adc-95a2-a4624b545779" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_RelatedPartyTransactionCostandExpenses_019dac15-a334-7e27-9aa1-972a95cb0848" xlink:href="optu-20260331.xsd#optu_RelatedPartyTransactionCostandExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019dac15-a334-717b-8e3e-ff89fbd6f9b3" xlink:to="loc_optu_RelatedPartyTransactionCostandExpenses_019dac15-a334-7e27-9aa1-972a95cb0848" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingCostsAndExpenses_019dac15-a334-7b30-b00b-b01896c9ce48" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingCostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7d6b-a0b2-0ec1b59b01e2" xlink:to="loc_us-gaap_OperatingCostsAndExpenses_019dac15-a334-7b30-b00b-b01896c9ce48" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty_019dac15-a334-76d7-94cd-a20865f5638c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7d6b-a0b2-0ec1b59b01e2" xlink:to="loc_us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty_019dac15-a334-76d7-94cd-a20865f5638c" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/AFFILIATEANDRELATEDPARTYTRANSACTIONSAmountsDueFromandDuetoRelatedPartiesDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#AFFILIATEANDRELATEDPARTYTRANSACTIONSAmountsDueFromandDuetoRelatedPartiesDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/AFFILIATEANDRELATEDPARTYTRANSACTIONSAmountsDueFromandDuetoRelatedPartiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7e8e-864f-a53227b54a56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dac15-a334-7c3f-8846-9bdc431f36fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7e8e-864f-a53227b54a56" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dac15-a334-7c3f-8846-9bdc431f36fc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-715f-8605-8c3b05c42f18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dac15-a334-7c3f-8846-9bdc431f36fc" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-715f-8605-8c3b05c42f18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a334-715f-8605-8c3b05c42f18_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-715f-8605-8c3b05c42f18" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a334-715f-8605-8c3b05c42f18_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a334-715a-8983-dfdcbe1a89e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-715f-8605-8c3b05c42f18" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a334-715a-8983-dfdcbe1a89e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dac15-a334-7e4e-95f3-f63742f0b5c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019dac15-a334-715a-8983-dfdcbe1a89e7" xlink:to="loc_us-gaap_RelatedPartyMember_019dac15-a334-7e4e-95f3-f63742f0b5c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019dac15-a334-729f-ace3-ebf521f6dc41" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dac15-a334-7c3f-8846-9bdc431f36fc" xlink:to="loc_srt_CounterpartyNameAxis_019dac15-a334-729f-ace3-ebf521f6dc41" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dac15-a334-729f-ace3-ebf521f6dc41_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019dac15-a334-729f-ace3-ebf521f6dc41" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dac15-a334-729f-ace3-ebf521f6dc41_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dac15-a334-75bf-82f8-a532d597b561" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019dac15-a334-729f-ace3-ebf521f6dc41" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dac15-a334-75bf-82f8-a532d597b561" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_AlticeEuropeMember_019dac15-a334-709c-8d31-944580fd9ae9" xlink:href="optu-20260331.xsd#optu_AlticeEuropeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dac15-a334-75bf-82f8-a532d597b561" xlink:to="loc_optu_AlticeEuropeMember_019dac15-a334-709c-8d31-944580fd9ae9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_OtherRelatedPartyMember_019dac15-a334-7195-8ca9-bd35035c1bae" xlink:href="optu-20260331.xsd#optu_OtherRelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dac15-a334-75bf-82f8-a532d597b561" xlink:to="loc_optu_OtherRelatedPartyMember_019dac15-a334-7195-8ca9-bd35035c1bae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019dac15-a334-7b65-82f3-517d57807f15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dac15-a334-7c3f-8846-9bdc431f36fc" xlink:to="loc_us-gaap_AwardTypeAxis_019dac15-a334-7b65-82f3-517d57807f15" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7b65-82f3-517d57807f15_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019dac15-a334-7b65-82f3-517d57807f15" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7b65-82f3-517d57807f15_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7d5f-9ac9-641e1373de87" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019dac15-a334-7b65-82f3-517d57807f15" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7d5f-9ac9-641e1373de87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019dac15-a334-7a52-b78b-cdcb818bc6d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019dac15-a334-7d5f-9ac9-641e1373de87" xlink:to="loc_us-gaap_PerformanceSharesMember_019dac15-a334-7a52-b78b-cdcb818bc6d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019dac15-a334-7389-ac80-5d1d7c82d3e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dac15-a334-7c3f-8846-9bdc431f36fc" xlink:to="loc_us-gaap_PlanNameAxis_019dac15-a334-7389-ac80-5d1d7c82d3e0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019dac15-a334-7389-ac80-5d1d7c82d3e0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019dac15-a334-7389-ac80-5d1d7c82d3e0" xlink:to="loc_us-gaap_PlanNameDomain_019dac15-a334-7389-ac80-5d1d7c82d3e0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019dac15-a334-7975-b0cf-2cb76d6a61b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019dac15-a334-7389-ac80-5d1d7c82d3e0" xlink:to="loc_us-gaap_PlanNameDomain_019dac15-a334-7975-b0cf-2cb76d6a61b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_A2017LTIPMember_019dac15-a334-79e9-86e5-ac86c5d6bf86" xlink:href="optu-20260331.xsd#optu_A2017LTIPMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019dac15-a334-7975-b0cf-2cb76d6a61b1" xlink:to="loc_optu_A2017LTIPMember_019dac15-a334-79e9-86e5-ac86c5d6bf86" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019dac15-a334-73c8-938b-6efbeed7c9c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7e8e-864f-a53227b54a56" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019dac15-a334-73c8-938b-6efbeed7c9c4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesCurrent_019dac15-a334-7edc-8286-d1bdee17bb92" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7e8e-864f-a53227b54a56" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesCurrent_019dac15-a334-7edc-8286-d1bdee17bb92" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/AFFILIATEANDRELATEDPARTYTRANSACTIONSNarrativeDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#AFFILIATEANDRELATEDPARTYTRANSACTIONSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/AFFILIATEANDRELATEDPARTYTRANSACTIONSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7f81-9525-45a0b6c5899e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dac15-a334-7d72-b75b-67c05f8971ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7f81-9525-45a0b6c5899e" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dac15-a334-7d72-b75b-67c05f8971ca" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a334-71e3-a189-2bda6b1796c9" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dac15-a334-7d72-b75b-67c05f8971ca" xlink:to="loc_dei_LegalEntityAxis_019dac15-a334-71e3-a189-2bda6b1796c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a334-71e3-a189-2bda6b1796c9_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a334-71e3-a189-2bda6b1796c9" xlink:to="loc_dei_EntityDomain_019dac15-a334-71e3-a189-2bda6b1796c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a334-73c1-b7c7-16410026daca" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a334-71e3-a189-2bda6b1796c9" xlink:to="loc_dei_EntityDomain_019dac15-a334-73c1-b7c7-16410026daca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsMember_019dac15-a334-7745-91f1-a4d062fcee69" xlink:href="optu-20260331.xsd#optu_CSCHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a334-73c1-b7c7-16410026daca" xlink:to="loc_optu_CSCHoldingsMember_019dac15-a334-7745-91f1-a4d062fcee69" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_I24NewsMember_019de461-1e60-7e91-9707-31b550c8fca9" xlink:href="optu-20260331.xsd#optu_I24NewsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a334-73c1-b7c7-16410026daca" xlink:to="loc_optu_I24NewsMember_019de461-1e60-7e91-9707-31b550c8fca9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019dac15-a334-7792-bb52-5ddf9a96a8f0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dac15-a334-7d72-b75b-67c05f8971ca" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019dac15-a334-7792-bb52-5ddf9a96a8f0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dac15-a334-7792-bb52-5ddf9a96a8f0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dac15-a334-7792-bb52-5ddf9a96a8f0" xlink:to="loc_us-gaap_EquityComponentDomain_019dac15-a334-7792-bb52-5ddf9a96a8f0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dac15-a334-7bdb-9a14-fff5ea8925fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dac15-a334-7792-bb52-5ddf9a96a8f0" xlink:to="loc_us-gaap_EquityComponentDomain_019dac15-a334-7bdb-9a14-fff5ea8925fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019dac15-a334-7917-98a5-171fa4838e12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dac15-a334-7bdb-9a14-fff5ea8925fa" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019dac15-a334-7917-98a5-171fa4838e12" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019dac15-a334-7ecd-a46b-2eab1944a25d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dac15-a334-7d72-b75b-67c05f8971ca" xlink:to="loc_srt_CounterpartyNameAxis_019dac15-a334-7ecd-a46b-2eab1944a25d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dac15-a334-7ecd-a46b-2eab1944a25d_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019dac15-a334-7ecd-a46b-2eab1944a25d" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dac15-a334-7ecd-a46b-2eab1944a25d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dac15-a334-7fce-98fe-1eeb2a868d7e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019dac15-a334-7ecd-a46b-2eab1944a25d" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dac15-a334-7fce-98fe-1eeb2a868d7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CaptiveMember_019dac15-a334-7484-a881-a1554dbef01a" xlink:href="optu-20260331.xsd#optu_CaptiveMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dac15-a334-7fce-98fe-1eeb2a868d7e" xlink:to="loc_optu_CaptiveMember_019dac15-a334-7484-a881-a1554dbef01a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-74be-8c14-407cca99ec60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dac15-a334-7d72-b75b-67c05f8971ca" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-74be-8c14-407cca99ec60" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a334-74be-8c14-407cca99ec60_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-74be-8c14-407cca99ec60" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a334-74be-8c14-407cca99ec60_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a334-7a6c-870b-d15f87f862e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a334-74be-8c14-407cca99ec60" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a334-7a6c-870b-d15f87f862e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dac15-a334-7921-9f08-e9d1e34e2aad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019dac15-a334-7a6c-870b-d15f87f862e4" xlink:to="loc_us-gaap_RelatedPartyMember_019dac15-a334-7921-9f08-e9d1e34e2aad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CaptiveMember_019dac15-a334-7477-8768-24e241e2dc8d" xlink:href="optu-20260331.xsd#optu_CaptiveMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019dac15-a334-7a6c-870b-d15f87f862e4" xlink:to="loc_optu_CaptiveMember_019dac15-a334-7477-8768-24e241e2dc8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_AlticeUSAMember_019dac15-a334-7e08-a3d9-d93b98f5be22" xlink:href="optu-20260331.xsd#optu_AlticeUSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019dac15-a334-7a6c-870b-d15f87f862e4" xlink:to="loc_optu_AlticeUSAMember_019dac15-a334-7e08-a3d9-d93b98f5be22" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCash_019dac15-a334-7e3c-828a-4af1b5709b04" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7f81-9525-45a0b6c5899e" xlink:to="loc_us-gaap_DividendsCash_019dac15-a334-7e3c-828a-4af1b5709b04" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_NonCashDistributionsToParent_019dac15-a334-7c2c-9c1c-c5524d375935" xlink:href="optu-20260331.xsd#optu_NonCashDistributionsToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7f81-9525-45a0b6c5899e" xlink:to="loc_optu_NonCashDistributionsToParent_019dac15-a334-7c2c-9c1c-c5524d375935" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayable_019dac15-a334-7cf2-993d-27bb1fd4c7df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7f81-9525-45a0b6c5899e" xlink:to="loc_us-gaap_NotesPayable_019dac15-a334-7cf2-993d-27bb1fd4c7df" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherReceivables_019dac15-a334-7848-b218-a85247997f22" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7f81-9525-45a0b6c5899e" xlink:to="loc_us-gaap_OtherReceivables_019dac15-a334-7848-b218-a85247997f22" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPaidNet_019dac15-a334-7ab4-bf08-e373ffdb18ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7f81-9525-45a0b6c5899e" xlink:to="loc_us-gaap_InterestPaidNet_019dac15-a334-7ab4-bf08-e373ffdb18ea" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_019de460-a19d-75e3-86fa-233fba063022" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromDivestitureOfBusinesses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7f81-9525-45a0b6c5899e" xlink:to="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_019de460-a19d-75e3-86fa-233fba063022" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_MaximumReimbursementOfCertainLiabilities_019de465-1bee-7fb7-a9dc-2b4cded28dd4" xlink:href="optu-20260331.xsd#optu_MaximumReimbursementOfCertainLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7f81-9525-45a0b6c5899e" xlink:to="loc_optu_MaximumReimbursementOfCertainLiabilities_019de465-1bee-7fb7-a9dc-2b4cded28dd4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_AmountOfReimbursementRecordedThroughEquity_019de466-c0af-73e6-b7b1-c7ea4b80c515" xlink:href="optu-20260331.xsd#optu_AmountOfReimbursementRecordedThroughEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dac15-a334-7f81-9525-45a0b6c5899e" xlink:to="loc_optu_AmountOfReimbursementRecordedThroughEquity_019de466-c0af-73e6-b7b1-c7ea4b80c515" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/COMMITMENTSANDCONTINGENCIESNarrativeDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#COMMITMENTSANDCONTINGENCIESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/COMMITMENTSANDCONTINGENCIESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_019dac15-a334-75fc-91e0-ab017e96b91c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_019dac15-a334-7294-ba1e-502ac0034a4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_019dac15-a334-75fc-91e0-ab017e96b91c" xlink:to="loc_us-gaap_LossContingenciesTable_019dac15-a334-7294-ba1e-502ac0034a4f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseAxis_019dac15-a334-7e65-8f44-af0332b7d2ef" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019dac15-a334-7294-ba1e-502ac0034a4f" xlink:to="loc_srt_LitigationCaseAxis_019dac15-a334-7e65-8f44-af0332b7d2ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_019dac15-a334-7e65-8f44-af0332b7d2ef_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_LitigationCaseAxis_019dac15-a334-7e65-8f44-af0332b7d2ef" xlink:to="loc_srt_LitigationCaseTypeDomain_019dac15-a334-7e65-8f44-af0332b7d2ef_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_019dac15-a334-7003-a6f6-b5bb1fddc8b6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_LitigationCaseAxis_019dac15-a334-7e65-8f44-af0332b7d2ef" xlink:to="loc_srt_LitigationCaseTypeDomain_019dac15-a334-7003-a6f6-b5bb1fddc8b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_WarnerMatterMember_019dac15-a334-7c28-86c9-014b4d7b7d56" xlink:href="optu-20260331.xsd#optu_WarnerMatterMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_LitigationCaseTypeDomain_019dac15-a334-7003-a6f6-b5bb1fddc8b6" xlink:to="loc_optu_WarnerMatterMember_019dac15-a334-7c28-86c9-014b4d7b7d56" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_AmountOfCopyrightedWorksInfringedOn_019dac15-a334-7464-8a7e-e8936b42e768" xlink:href="optu-20260331.xsd#optu_AmountOfCopyrightedWorksInfringedOn"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019dac15-a334-75fc-91e0-ab017e96b91c" xlink:to="loc_optu_AmountOfCopyrightedWorksInfringedOn_019dac15-a334-7464-8a7e-e8936b42e768" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/SegmentReportingDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#SegmentReportingDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/SegmentReportingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019dac15-a335-7756-a883-ae185df6b1ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dac15-a335-7c72-9a47-268ae1a44dc9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dac15-a335-7756-a883-ae185df6b1ff" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dac15-a335-7c72-9a47-268ae1a44dc9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019dac15-a335-7d5a-9c7f-e11efabc2ff8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dac15-a335-7c72-9a47-268ae1a44dc9" xlink:to="loc_srt_CounterpartyNameAxis_019dac15-a335-7d5a-9c7f-e11efabc2ff8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dac15-a335-7d5a-9c7f-e11efabc2ff8_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019dac15-a335-7d5a-9c7f-e11efabc2ff8" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dac15-a335-7d5a-9c7f-e11efabc2ff8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dac15-a335-730f-b684-466efb7264b5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019dac15-a335-7d5a-9c7f-e11efabc2ff8" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dac15-a335-730f-b684-466efb7264b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CaptiveMember_019dac15-a335-7e1f-a2f8-e0740439d869" xlink:href="optu-20260331.xsd#optu_CaptiveMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dac15-a335-730f-b684-466efb7264b5" xlink:to="loc_optu_CaptiveMember_019dac15-a335-7e1f-a2f8-e0740439d869" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a335-7dab-8db3-9d8fa259bd4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dac15-a335-7c72-9a47-268ae1a44dc9" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a335-7dab-8db3-9d8fa259bd4c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a335-7dab-8db3-9d8fa259bd4c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a335-7dab-8db3-9d8fa259bd4c" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a335-7dab-8db3-9d8fa259bd4c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dac15-a335-7e18-89da-bf4ff310984d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dac15-a335-7dab-8db3-9d8fa259bd4c" xlink:to="loc_us-gaap_RelatedPartyDomain_019dac15-a335-7e18-89da-bf4ff310984d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dac15-a335-726f-ab7c-96ada4ad655a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019dac15-a335-7e18-89da-bf4ff310984d" xlink:to="loc_us-gaap_RelatedPartyMember_019dac15-a335-726f-ab7c-96ada4ad655a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCostAndExpenseOperating_019dac15-a335-70b4-942f-8d2771bc2e40" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCostAndExpenseOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dac15-a335-7756-a883-ae185df6b1ff" xlink:to="loc_us-gaap_OtherCostAndExpenseOperating_019dac15-a335-70b4-942f-8d2771bc2e40" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.optimum.com/role/SUPPLEMENTALSCHEDULESDetails" xlink:type="simple" xlink:href="optu-20260331.xsd#SUPPLEMENTALSCHEDULESDetails"/>
  <link:definitionLink xlink:role="http://www.optimum.com/role/SUPPLEMENTALSCHEDULESDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_srt_CondensedBalanceSheetStatementsCaptionsLineItems_019dac15-a335-7fdb-a243-34cc6f7b3e90" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CondensedBalanceSheetStatementsCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CondensedBalanceSheetStatementTable_019dac15-a335-7971-9259-5ae6498f8dc1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CondensedBalanceSheetStatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_CondensedBalanceSheetStatementsCaptionsLineItems_019dac15-a335-7fdb-a243-34cc6f7b3e90" xlink:to="loc_srt_CondensedBalanceSheetStatementTable_019dac15-a335-7971-9259-5ae6498f8dc1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dac15-a335-7143-ba8b-af944bf7b579" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_CondensedBalanceSheetStatementTable_019dac15-a335-7971-9259-5ae6498f8dc1" xlink:to="loc_dei_LegalEntityAxis_019dac15-a335-7143-ba8b-af944bf7b579" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a335-7143-ba8b-af944bf7b579_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dac15-a335-7143-ba8b-af944bf7b579" xlink:to="loc_dei_EntityDomain_019dac15-a335-7143-ba8b-af944bf7b579_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dac15-a335-71fc-a72c-f534ec5ac61d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dac15-a335-7143-ba8b-af944bf7b579" xlink:to="loc_dei_EntityDomain_019dac15-a335-71fc-a72c-f534ec5ac61d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsMember_019dac15-a335-74d7-9976-93ceab615096" xlink:href="optu-20260331.xsd#optu_CSCHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dac15-a335-71fc-a72c-f534ec5ac61d" xlink:to="loc_optu_CSCHoldingsMember_019dac15-a335-74d7-9976-93ceab615096" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dac15-a335-7ad9-bb66-ebc38c4c702f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_CondensedBalanceSheetStatementTable_019dac15-a335-7971-9259-5ae6498f8dc1" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dac15-a335-7ad9-bb66-ebc38c4c702f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dac15-a335-7ad9-bb66-ebc38c4c702f_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dac15-a335-7ad9-bb66-ebc38c4c702f" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dac15-a335-7ad9-bb66-ebc38c4c702f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dac15-a335-7e17-a9d4-bebdced3c1da" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dac15-a335-7ad9-bb66-ebc38c4c702f" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dac15-a335-7e17-a9d4-bebdced3c1da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_CSCHoldingsRestrictedGroupMember_019dac15-a335-75fb-a488-6e453d768344" xlink:href="optu-20260331.xsd#optu_CSCHoldingsRestrictedGroupMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dac15-a335-7e17-a9d4-bebdced3c1da" xlink:to="loc_optu_CSCHoldingsRestrictedGroupMember_019dac15-a335-75fb-a488-6e453d768344" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_UnrestrictedGroupMember_019dac15-a335-7005-8ea2-dd6994ba7ba9" xlink:href="optu-20260331.xsd#optu_UnrestrictedGroupMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dac15-a335-7e17-a9d4-bebdced3c1da" xlink:to="loc_optu_UnrestrictedGroupMember_019dac15-a335-7005-8ea2-dd6994ba7ba9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationEliminationsMember_019dac15-a335-7737-a2dd-b3d21e09f79e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationEliminationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dac15-a335-7e17-a9d4-bebdced3c1da" xlink:to="loc_srt_ConsolidationEliminationsMember_019dac15-a335-7737-a2dd-b3d21e09f79e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetRelatedDisclosuresAbstract_019dac15-a335-767b-899f-92bfc39d96ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BalanceSheetRelatedDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedBalanceSheetStatementsCaptionsLineItems_019dac15-a335-7fdb-a243-34cc6f7b3e90" xlink:to="loc_us-gaap_BalanceSheetRelatedDisclosuresAbstract_019dac15-a335-767b-899f-92bfc39d96ac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_019dac15-a335-7cb0-8943-41e591539aa1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetRelatedDisclosuresAbstract_019dac15-a335-767b-899f-92bfc39d96ac" xlink:to="loc_us-gaap_AssetsCurrent_019dac15-a335-7cb0-8943-41e591539aa1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_AssetsLongTerm_019dac15-a335-71c3-ad49-85dea11208db" xlink:href="optu-20260331.xsd#optu_AssetsLongTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetRelatedDisclosuresAbstract_019dac15-a335-767b-899f-92bfc39d96ac" xlink:to="loc_optu_AssetsLongTerm_019dac15-a335-71c3-ad49-85dea11208db" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019dac15-a335-79f0-9e17-abd248824edf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetRelatedDisclosuresAbstract_019dac15-a335-767b-899f-92bfc39d96ac" xlink:to="loc_us-gaap_Assets_019dac15-a335-79f0-9e17-abd248824edf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_019dac15-a335-7a15-9ce7-ac596fd24c31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetRelatedDisclosuresAbstract_019dac15-a335-767b-899f-92bfc39d96ac" xlink:to="loc_us-gaap_LiabilitiesCurrent_019dac15-a335-7a15-9ce7-ac596fd24c31" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019dac15-a335-779b-8d89-6c655a58c7c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetRelatedDisclosuresAbstract_019dac15-a335-767b-899f-92bfc39d96ac" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019dac15-a335-779b-8d89-6c655a58c7c5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesOtherThanLongtermDebtNoncurrent_019dac15-a335-76f6-81bc-3f55f49fa676" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesOtherThanLongtermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetRelatedDisclosuresAbstract_019dac15-a335-767b-899f-92bfc39d96ac" xlink:to="loc_us-gaap_LiabilitiesOtherThanLongtermDebtNoncurrent_019dac15-a335-76f6-81bc-3f55f49fa676" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019dac15-a335-7a3e-b19d-f4e253b9512f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetRelatedDisclosuresAbstract_019dac15-a335-767b-899f-92bfc39d96ac" xlink:to="loc_us-gaap_Liabilities_019dac15-a335-7a3e-b19d-f4e253b9512f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_optu_Membershipequitybeforenoncontrollinginterest_019dac15-a335-7650-8e88-97ec2cf6ab64" xlink:href="optu-20260331.xsd#optu_Membershipequitybeforenoncontrollinginterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetRelatedDisclosuresAbstract_019dac15-a335-767b-899f-92bfc39d96ac" xlink:to="loc_optu_Membershipequitybeforenoncontrollinginterest_019dac15-a335-7650-8e88-97ec2cf6ab64" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterest_019dac15-a335-78b9-b869-ac00f6d72a80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetRelatedDisclosuresAbstract_019dac15-a335-767b-899f-92bfc39d96ac" xlink:to="loc_us-gaap_MinorityInterest_019dac15-a335-78b9-b869-ac00f6d72a80" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_019dac15-a335-77c7-903c-c659bfa0d33f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetRelatedDisclosuresAbstract_019dac15-a335-767b-899f-92bfc39d96ac" xlink:to="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_019dac15-a335-77c7-903c-c659bfa0d33f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_019dac15-a335-710a-bbcf-46c0eb638e49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetRelatedDisclosuresAbstract_019dac15-a335-767b-899f-92bfc39d96ac" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_019dac15-a335-710a-bbcf-46c0eb638e49" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementAbstract_019dac15-a3f9-7b69-b46c-631ec16bbbcd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedBalanceSheetStatementsCaptionsLineItems_019dac15-a335-7fdb-a243-34cc6f7b3e90" xlink:to="loc_us-gaap_IncomeStatementAbstract_019dac15-a3f9-7b69-b46c-631ec16bbbcd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019dac15-a3f9-7c7e-9860-c658f8fadff8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementAbstract_019dac15-a3f9-7b69-b46c-631ec16bbbcd" xlink:to="loc_us-gaap_Revenues_019dac15-a3f9-7c7e-9860-c658f8fadff8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_019dac15-a3f9-7f0a-bb39-95bceb2fe6c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementAbstract_019dac15-a3f9-7b69-b46c-631ec16bbbcd" xlink:to="loc_us-gaap_CostsAndExpenses_019dac15-a3f9-7f0a-bb39-95bceb2fe6c8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019dac15-a3f9-7abd-9f93-2468c50a5f35" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementAbstract_019dac15-a3f9-7b69-b46c-631ec16bbbcd" xlink:to="loc_us-gaap_OperatingIncomeLoss_019dac15-a3f9-7abd-9f93-2468c50a5f35" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_019dac15-a3f9-7803-be79-1ffc3f19b0ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementAbstract_019dac15-a3f9-7b69-b46c-631ec16bbbcd" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_019dac15-a3f9-7803-be79-1ffc3f19b0ae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019dac15-a3f9-7239-beae-d4b611cccd76" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementAbstract_019dac15-a3f9-7b69-b46c-631ec16bbbcd" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019dac15-a3f9-7239-beae-d4b611cccd76" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019dac15-a3f9-7982-9436-1dab216122d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementAbstract_019dac15-a3f9-7b69-b46c-631ec16bbbcd" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019dac15-a3f9-7982-9436-1dab216122d4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019dac15-a3f9-7b32-8ab8-423c50838c2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementAbstract_019dac15-a3f9-7b69-b46c-631ec16bbbcd" xlink:to="loc_us-gaap_ProfitLoss_019dac15-a3f9-7b32-8ab8-423c50838c2e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_019dac15-a3f9-7f44-b6cf-7b505975d3c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementAbstract_019dac15-a3f9-7b69-b46c-631ec16bbbcd" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_019dac15-a3f9-7f44-b6cf-7b505975d3c1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019dac15-a3f9-793f-b106-52332cf9e180" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementAbstract_019dac15-a3f9-7b69-b46c-631ec16bbbcd" xlink:to="loc_us-gaap_NetIncomeLoss_019dac15-a3f9-793f-b106-52332cf9e180" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillAndIntangibleAssetImpairment_019de587-af04-7994-a757-7fb2a58c03f0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillAndIntangibleAssetImpairment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedBalanceSheetStatementsCaptionsLineItems_019dac15-a335-7fdb-a243-34cc6f7b3e90" xlink:to="loc_us-gaap_GoodwillAndIntangibleAssetImpairment_019de587-af04-7994-a757-7fb2a58c03f0" xlink:type="arc" order="2"/>
  </link:definitionLink>
</link:linkbase>
