<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0407</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2023-03-31</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001095651</issuerCik>
        <issuerName>ISTAR INC.</issuerName>
        <issuerTradingSymbol>SAFE</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000936828</rptOwnerCik>
            <rptOwnerName>GIC Private Ltd</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>168 ROBINSON ROAD</rptOwnerStreet1>
            <rptOwnerStreet2>#37-01 CAPITAL TOWER</rptOwnerStreet2>
            <rptOwnerCity>SINGAPORE</rptOwnerCity>
            <rptOwnerState>U0</rptOwnerState>
            <rptOwnerZipCode>068912</rptOwnerZipCode>
            <rptOwnerStateDescription>SINGAPORE</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001709755</rptOwnerCik>
            <rptOwnerName>GIC Real Estate Private Ltd</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O GIC PRIVATE LIMITED</rptOwnerStreet1>
            <rptOwnerStreet2>168 ROBINSON ROAD, #37-01 CAPITAL TOWER</rptOwnerStreet2>
            <rptOwnerCity>SINGAPORE</rptOwnerCity>
            <rptOwnerState>U0</rptOwnerState>
            <rptOwnerZipCode>068912</rptOwnerZipCode>
            <rptOwnerStateDescription>SINGAPORE</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001709752</rptOwnerCik>
            <rptOwnerName>GIC Real Estate, Inc.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>ONE BUSH STREET, SUITE 1000</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SAN FRANCISCO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94104</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001709649</rptOwnerCik>
            <rptOwnerName>SFTY Venture LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O GIC REAL ESTATE, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>280 PARK AVENUE, 9TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10017</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2023-03-31</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2123435</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2123435</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2023-03-31</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2125000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2125000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Reflects securities acquired pursuant to the terms that certain Agreement and Plan of Merger, dated as of August 10, 2022 (the &quot;Merger Agreement&quot;), entered into by and among Safehold Inc. (&quot;Old Safehold&quot;) and iStar Inc. (the &quot;Issuer&quot;).  Pursuant to the Merger Agreement, the Issuer merged with and into iStar, with iStar surviving the merger (the &quot;Merger&quot;) and changing its name to &quot;Safehold Inc.&quot;  Pursuant to the terms of the Merger Agreement, each Old Safehold share of common stock outstanding immediately prior to the effective time of the Merger (other than certain excluded shares) automatically converted into the right to receive one newly issued share of Issuer common stock.</footnote>
        <footnote id="F2">Reflects securities held directly by GIC Private Limited.</footnote>
        <footnote id="F3">GIC Real Estate, Inc., the investment manager for SFTY Venture LLC, has the power to vote and dispose of such shares. GIC Real Estate, Inc. shares such powers with GIC Real Estate Private Limited and GIC Private Limited. Each of the Reporting Persons disclaims beneficial ownership of these shares, except to the extent of its pecuniary interest therein, if any.</footnote>
        <footnote id="F4">Reflects securities held directly by SFTY Venture LLC.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>GIC PRIVATE LIMITED, By: /s/ Glien Tan Cheng Chuan, Name: Glien Tan Cheng Chuan, Title: Managing Director; By: /s/ Toh Tze Meng, Name: Toh Tze Meng, Title: Senior Vice President</signatureName>
        <signatureDate>2023-04-04</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>GIC REAL ESTATE PRIVATE LIMITED, By: /s/ Chan Hoe Yin, Name: Chan Hoe Yin, Title: Director</signatureName>
        <signatureDate>2023-04-04</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>GIC REAL ESTATE, INC., By: /s/ Kristin Leung, Name: Kristin Leung, Title: Managing Director</signatureName>
        <signatureDate>2023-04-04</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>SFTY VENTURE LLC, By: /s/ Kristin Leung, Name: Kristin Leung, Title: Managing Director</signatureName>
        <signatureDate>2023-04-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
