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

    <schemaVersion>X0609</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2026-06-30</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001699963</issuerCik>
        <issuerName>Neutron Holdings, Inc.</issuerName>
        <issuerTradingSymbol>LIME</issuerTradingSymbol>
        <issuerForeignTradingSymbol></issuerForeignTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001543151</rptOwnerCik>
            <rptOwnerName>Uber Technologies, Inc</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerNonUSAddressFlag>false</rptOwnerNonUSAddressFlag>
            <rptOwnerStreet1>1725 3RD STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SAN FRANCISCO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94158</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

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                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>6329623</value>
                </transactionShares>
                <transactionPricePerShare>
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                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
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                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
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                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
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        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
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                <value>2026-06-30</value>
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                </transactionShares>
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                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
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                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
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                    <value>D</value>
                </directOrIndirectOwnership>
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        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
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            <transactionDate>
                <value>2026-07-02</value>
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                <equitySwapInvolved>0</equitySwapInvolved>
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                <transactionShares>
                    <value>1063742</value>
                </transactionShares>
                <transactionPricePerShare>
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                </sharesOwnedFollowingTransaction>
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        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
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            <transactionDate>
                <value>2026-07-02</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>800000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>25.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
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                <sharesOwnedFollowingTransaction>
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                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Convertible Notes</value>
            </securityTitle>
            <conversionOrExercisePrice>
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            <transactionDate>
                <value>2026-06-30</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>C</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>6329623</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F1"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>6329623</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Convertible Notes</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2026-06-30</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>C</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3271983</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
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                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
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                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>3271983</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
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                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
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                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Series C Preferred Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F3"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2026-07-02</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
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                <transactionFormType>4</transactionFormType>
                <transactionCode>C</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1063742</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
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                    <value>D</value>
                </transactionAcquiredDisposedCode>
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                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1063742</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
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                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
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        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">On May 7, 2020, the Issuer issued to the Reporting Person convertible notes in the aggregate principal amount of approximately $85 million (the &quot;2020 Notes&quot;). The 2020 Notes accrue non-compounding interest at a rate of 4.0% per annum and mature seven years following the date of issuance, unless earlier converted pursuant to their terms. At the execution of the underwriting agreement in connection with the IPO, the aggregate outstanding principal balance of the 2020 Notes plus any accrued and unpaid interest automatically converted into shares of Common Stock at a ratio based on a conversion price equal to $340.0 million plus any consideration paid by each noteholder for the 2020 Notes divided by the Issuer's fully-diluted capitalization on August 5, 2020.</footnote>
        <footnote id="F2">On October 29, 2021, the Issuer issued to the Reporting Person convertible notes in the aggregate principal amount of approximately $50 million (the &quot;2021 Notes&quot;). The 2021 Notes initially accrued interest at a rate of 4.0% per annum, which increased by 0.5% in April 2023, and thereafter increasing by 1.0% at every successive six month interval, up to a maximum rate of 8.0%. The 2021 Notes mature on October 29, 2026, unless earlier converted pursuant to their terms. At the execution of the underwriting agreement in connection with the IPO, the aggregate outstanding principal balance of the 2021 Notes plus any accrued and unpaid interest automatically converted into shares of Common Stock based on a conversion price equal to the lesser of (i) 80% of the IPO price per share of Common Stock and (ii) a specified valuation cap of $1.5 billion divided by the aggregate amount of fully diluted shares of Common Stock on the applicable conversion date as set forth in the 2021 Notes.</footnote>
        <footnote id="F3">Each share of the Issuer's convertible preferred stock automatically converted into one share of Common Stock upon the closing of the Issuer's initial public offering (the &quot;IPO&quot;).</footnote>
        <footnote id="F4">Prior to the closing of the IPO, the Reporting Person distributed all of its shares to SMB Holding Corporation, a wholly-owned subsidiary, in a transaction exempt from reporting pursuant to Rule 16a-13.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Elizabeth Coleman, Vice President, Deputy General Counsel and Deputy Corporate Secretary</signatureName>
        <signatureDate>2026-07-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
