<SEC-DOCUMENT>0001213900-24-029525.txt : 20240402
<SEC-HEADER>0001213900-24-029525.hdr.sgml : 20240402
<ACCEPTANCE-DATETIME>20240402200029
ACCESSION NUMBER:		0001213900-24-029525
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20240331
FILED AS OF DATE:		20240402
DATE AS OF CHANGE:		20240402

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			ECP ControlCo, LLC
		CENTRAL INDEX KEY:			0001707921
		ORGANIZATION NAME:           	
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-38186
		FILM NUMBER:		24816478

	BUSINESS ADDRESS:	
		STREET 1:		40 BEECHWOOD ROAD
		CITY:			SUMMIT
		STATE:			NJ
		ZIP:			07901
		BUSINESS PHONE:		(973) 671-6100

	MAIL ADDRESS:	
		STREET 1:		40 BEECHWOOD ROAD
		CITY:			SUMMIT
		STATE:			NJ
		ZIP:			07901

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Energy Capital Partners Management, LP
		CENTRAL INDEX KEY:			0001815150
		ORGANIZATION NAME:           	
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-38186
		FILM NUMBER:		24816476

	BUSINESS ADDRESS:	
		STREET 1:		51 JOHN F. KENNEDY PARKWAY
		STREET 2:		SUITE 200
		CITY:			SHORT HILLS
		STATE:			NJ
		ZIP:			07078
		BUSINESS PHONE:		(973) 671-6100

	MAIL ADDRESS:	
		STREET 1:		51 JOHN F. KENNEDY PARKWAY
		STREET 2:		SUITE 200
		CITY:			SHORT HILLS
		STATE:			NJ
		ZIP:			07078

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			ECP Management GP, LLC
		CENTRAL INDEX KEY:			0001815147
		ORGANIZATION NAME:           	
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-38186
		FILM NUMBER:		24816477

	BUSINESS ADDRESS:	
		STREET 1:		51 JOHN F. KENNEDY PARKWAY
		STREET 2:		SUITE 200
		CITY:			SHORT HILLS
		STATE:			NJ
		ZIP:			07078
		BUSINESS PHONE:		(973) 671-6100

	MAIL ADDRESS:	
		STREET 1:		51 JOHN F. KENNEDY PARKWAY
		STREET 2:		SUITE 200
		CITY:			SHORT HILLS
		STATE:			NJ
		ZIP:			07078

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Custom Truck One Source, Inc.
		CENTRAL INDEX KEY:			0001709682
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-EQUIPMENT RENTAL & LEASING, NEC [7359]
		ORGANIZATION NAME:           	07 Trade & Services
		IRS NUMBER:				000000000
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		7701 INDEPENDENCE AVENUE
		CITY:			KANSAS CITY
		STATE:			MO
		ZIP:			64125
		BUSINESS PHONE:		(816) 241-4888

	MAIL ADDRESS:	
		STREET 1:		7701 INDEPENDENCE AVENUE
		CITY:			KANSAS CITY
		STATE:			MO
		ZIP:			64125

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	NESCO HOLDINGS, INC.
		DATE OF NAME CHANGE:	20190730

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	Capitol Investment Corp. IV
		DATE OF NAME CHANGE:	20170619
</SEC-HEADER>
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<TYPE>4
<SEQUENCE>1
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<TEXT>
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<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2024-03-31</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001709682</issuerCik>
        <issuerName>Custom Truck One Source, Inc.</issuerName>
        <issuerTradingSymbol>CTOS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001707921</rptOwnerCik>
            <rptOwnerName>ECP ControlCo, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>40 BEECHWOOD ROAD,</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SUMMIT,</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07901</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001815147</rptOwnerCik>
            <rptOwnerName>ECP Management GP, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>40 BEECHWOOD ROAD,</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SUMMIT,</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07901</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001815150</rptOwnerCik>
            <rptOwnerName>Energy Capital Partners Management, LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>40 BEECHWOOD ROAD,</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SUMMIT,</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07901</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2024-03-31</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>18640</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>18640</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>25738988</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnotes</value>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Restricted Stock Unit</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2024-03-31</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>18640</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F5"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>18640</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Restricted Stock Unit</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2024-04-01</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>22218</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F6"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F6"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>22218</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>22218</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.</footnote>
        <footnote id="F2">Represents securities held directly by Energy Capital Partners Management, LP (&quot;ECP Management&quot;). ECP Management GP, LLC is the general partner of ECP Management and may be deemed to share beneficial ownership of the securities held by ECP Management. ECP ControlCo, LLC (&quot;ECP ControlCo&quot;) is the sole member of ECP Management GP, LLC. As a result, ECP ControlCo may be deemed to share beneficial ownership of the securities beneficially owned by ECP Management GP, LLC. The managing members of ECP ControlCo are Douglas Kimmelman, Andrew Singer, Peter Labbat, Tyler Reeder and Rahman D'Argenio all of whom collectively share the power to vote and dispose of the securities beneficially owned by ECP ControlCo. Each such individual disclaims beneficial ownership of such shares except to the extent of his pecuniary interest therein.</footnote>
        <footnote id="F3">Includes 21,238,988 shares held by NESCO Holdings, LP and 4,500,000 shares held by ECP Cardinal Holdings, LP (&quot;ECP Cardinal&quot;). The general partner of each of ECP Cardinal and NESCO Holdings, LP is NESCO Holdings GP, LLC. ECP Starlight Guarantor (Public), LP (&quot;ECP Starlight&quot;) and Energy Capital Partners III (NESCO Co-Invest), LP are the sole members of NESCO Holdings GP, LLC.</footnote>
        <footnote id="F4">ECP ControlCo is the sole member of Energy Capital Partners III, LLC, which is the general partner of (i) Energy Capital Partners GP III, LP, which is the general partner of each of Energy Capital Partners III, LP, Energy Capital Partners III-A, LP, Energy Capital Partners III-B, LP, Energy Capital Partners III-C, LP, and Energy Capital Partners III-D, LP (together, the &quot;ECP III Funds&quot;), which are the sole members of ECP Starlight Public GP, LLC, which is the general partner of ECP Starlight, and (ii) Energy Capital Partners GP III Co-Investment (NESCO), LLC, which is the general partner of Energy Capital Partners III (NESCO Co-Invest), LP. As a result, each of the foregoing entities may be deemed to share beneficial ownership of the shares of Common Stock held by ECP Cardinal and NESCO Holdings, LP.</footnote>
        <footnote id="F5">The restricted stock units vested in full on March 31, 2024.</footnote>
        <footnote id="F6">The restricted stock units will vest on March 31, 2025 and have no expiration date.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>ECP ControlCo, LLC By: /s/ Rahman D'Argenio, Managing Member</signatureName>
        <signatureDate>2024-04-02</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>ECP Management GP, LLC By: ECP ControlCo, LLC, its sole member By: /s/ Rahman D'Argenio, Managing Member</signatureName>
        <signatureDate>2024-04-02</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>ECP ControlCo, LLC By: ECP Management GP, LLC, its general partner By: ECP ControlCo, LLC, its sole member By: /s/ Rahman D'Argenio, Managing Member</signatureName>
        <signatureDate>2024-04-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
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</SEC-DOCUMENT>
