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  <schemaVersion>X0202</schemaVersion>
  <headerData>
    <submissionType>13F-HR</submissionType>
    <filerInfo>
      <liveTestFlag>LIVE</liveTestFlag>
      <flags>
        <confirmingCopyFlag>false</confirmingCopyFlag>
        <returnCopyFlag>false</returnCopyFlag>
        <overrideInternetFlag>false</overrideInternetFlag>
      </flags>
      <filer>
        <credentials>
          <cik>0000830588</cik>
          <ccc>XXXXXXXX</ccc>
        </credentials>
      </filer>
      <periodOfReport>03-31-2026</periodOfReport>
    </filerInfo>
  </headerData>
  <formData>
    <coverPage>
      <reportCalendarOrQuarter>03-31-2026</reportCalendarOrQuarter>
      <isAmendment>false</isAmendment>
      <filingManager>
        <name>SUMMIT PARTNERS L P</name>
        <address>
          <ns1:street1>222 BERKELEY STREET</ns1:street1>
          <ns1:street2>18TH FLOOR</ns1:street2>
          <ns1:city>BOSTON</ns1:city>
          <ns1:stateOrCountry>MA</ns1:stateOrCountry>
          <ns1:zipCode>02116</ns1:zipCode>
        </address>
      </filingManager>
      <reportType>13F HOLDINGS REPORT</reportType>
      <form13FFileNumber>028-11703</form13FFileNumber>
      <crdNumber>000135271</crdNumber>
      <secFileNumber>801-64273</secFileNumber>
      <provideInfoForInstruction5>Y</provideInfoForInstruction5>
      <additionalInformation>Please note the following with respect to the data provided in the Information Table. The total shares reported for AKA BRANDS HLDG CORP reflects the total shares held through a holding company controlled by Summit Partners, L.P. ("Summit"). The total proceeds related to the shares held by the holding company which Summit or its affiliates will be entitled to at liquidation may be lower than the value reported herein. The total shares reported for KLAVIYO, INC. reflect Class B shares held by Summit and its affiliates and are voluntarily being reported notwithstanding that they are not on the List of Section 13F Securities as of 03/31/2026.</additionalInformation>
    </coverPage>
    <signatureBlock>
      <name>ADAM H. HENNESSEY</name>
      <title>MEMBER OF SUMMIT MASTER COMPANY, LLC (GP OF SUMMIT)</title>
      <phone>617-824-1000</phone>
      <signature>/S/ ADAM H. HENNESSEY</signature>
      <city>BOSTON</city>
      <stateOrCountry>MA</stateOrCountry>
      <signatureDate>05-08-2026</signatureDate>
    </signatureBlock>
    <summaryPage>
      <otherIncludedManagersCount>0</otherIncludedManagersCount>
      <tableEntryTotal>7</tableEntryTotal>
      <tableValueTotal>670154351</tableValueTotal>
    </summaryPage>
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