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

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2024-07-12</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0000711772</issuerCik>
        <issuerName>CAMBRIDGE BANCORP</issuerName>
        <issuerTradingSymbol>CATC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001959574</rptOwnerCik>
            <rptOwnerName>Halberstadt Peter J.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O CAMBRIDGE BANCORP</rptOwnerStreet1>
            <rptOwnerStreet2>78 BLANCHARD ROAD, SUITE 400</rptOwnerStreet2>
            <rptOwnerCity>BURLINGTON</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>01803</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>SVP, Chief Credit Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2024-07-12</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3886</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </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>2024-07-12</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1329</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>ESOP</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Disposed of pursuant to the Agreement and Plan of Merger (the &quot;Merger Agreement&quot;) dated as of September 19, 2023, by and between Cambridge Bancorp (&quot;Cambridge&quot;), Cambridge Trust Company, Eastern Bankshares, Inc. (&quot;Eastern&quot;), Eastern Bank and Citadel MS 2023, Inc., in exchange for the right to receive (i) 14,878 shares of Eastern common stock, with a market value of $14.87 per share of Eastern common stock based on the closing price of Eastern common stock on July 12, 2024, (ii) 496 Eastern restricted stock awards and (iii) 3,886 Eastern restricted stock unit awards, and in the case of (ii) and (iii), with the same terms, restrictions and vesting schedules as such existing Cambridge restricted stock award and Cambridge restricted stock unit award, respectively.</footnote>
        <footnote id="F2">Disposed of pursuant to the Merger Agreement in exchange for the right to receive 6,587 shares of Eastern common stock, with a market value of $14.87 per share of Eastern common stock based on the closing price of Eastern common stock on July 12, 2024.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Joseph P. Sapienza, as Attorney-In Fact</signatureName>
        <signatureDate>2024-07-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
