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

    <schemaVersion>X0609</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2026-10-16</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0001637873</issuerCik>
        <issuerName>ACV Auctions Inc.</issuerName>
        <issuerTradingSymbol>ACVA</issuerTradingSymbol>
        <issuerForeignTradingSymbol></issuerForeignTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001851605</rptOwnerCik>
            <rptOwnerName>Hirsch Brian</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerNonUSAddressFlag>false</rptOwnerNonUSAddressFlag>
            <rptOwnerStreet1>C/O ACV AUCTIONS INC.</rptOwnerStreet1>
            <rptOwnerStreet2>640 ELLICOTT ST., SUITE 321</rptOwnerStreet2>
            <rptOwnerCity>BUFFALO</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>14203</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2026-10-16</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>U</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>127178</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2026-10-16</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>U</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1397090</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2026-10-16</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>U</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>465697</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Pursuant to the Agreement and Plan of Merger, dated September 10, 2026 (the &quot;Merger Agreement&quot;), by and among ACV Auctions Inc. (&quot;ACV&quot;), Copart, Inc. (&quot;Copart&quot;), and Apple Merger Sub, Inc., a wholly owned subsidiary of Copart (&quot;Merger Sub&quot;), the shares of common stock of ACV that were tendered to Merger Sub prior to the expiration time of the offer were exchanged for $10.50 per share (&quot;Merger Consideration&quot;), net to the seller in cash, without interest, subject to any required withholding tax. After completion of the tender offer, pursuant to the terms of the Merger Agreement, Merger Sub merged with and into ACV (the &quot;Merger&quot;), with ACV surviving the Merger as a wholly owned subsidiary of Copart.</footnote>
        <footnote id="F2">Pursuant to the terms of the Merger Agreement, each outstanding restricted stock unit award corresponding to shares of ACV common stock (each, an &quot;ACV RSU&quot;) held by the Reporting Person was canceled in consideration for the right to receive the Merger Consideration in respect of each share of ACV common stock then subject to the ACV RSU.</footnote>
        <footnote id="F3">The shares are held by Tribeca Venture Fund II, L.P. (&quot;TVFII&quot;). Tribeca Venture Partners II GP, LLC (&quot;TVP II GP&quot;) is the general partner of TVFII. The Reporting Person is a managing partner of TVP II GP. The Reporting Person disclaims beneficial ownership of the shares held by TVFII, except to the extent of his pecuniary interest, if any, and this report shall not be deemed an admission that the Reporting Person is the beneficial owner of such shares.</footnote>
        <footnote id="F4">The shares are held by Tribeca Venture Fund II New York, L.P. (&quot;TVFII NY&quot;). TVP II GP is the general partner of TVFII NY. The Reporting Person is a managing partner of TVP II GP. The Reporting Person disclaims beneficial ownership of the shares held by TVFII NY, except to the extent of his pecuniary interest, if any, and this report shall not be deemed an admission that the Reporting Person is the beneficial owner of such shares.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Michelle Webb, Attorney-in-Fact</signatureName>
        <signatureDate>2026-10-19</signatureDate>
    </ownerSignature>
</ownershipDocument>
