Sec Form 4 Filing - PLATINUM EQUITY LLC @ Custom Truck One Source, Inc. - 2021-04-01

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person PLATINUM EQUITY LLC 2. Issuer Name and Ticker or Trading Symbol Custom Truck One Source, Inc. [ CTOS] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O PLATINUM EQUITY ADVISORS, LLC, 360 NORTH CRESCENT DRIVE, SOUTH BUILDING 3. Date of Earliest Transaction (MM/DD/YY) 04/01/2021 (Street) BEVERLY HILLS, CA90210 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 04/01/2021 P 148,600,000 D $ 5 148,600,000 I ( 1 ) ( 2 ) ( 3 ) ( 4 ) ( 5 ) See Footnotes ( 1 ) ( 2 ) ( 3 ) ( 4 ) ( 5 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other PLATINUM EQUITY LLC C/O PLATINUM EQUITY ADVISORS, LLC 360 NORTH CRESCENT DRIVE, SOUTH BUILDING BEVERLY HILLS, CA90210 X Gores Tom C/O PLATINUM EQUITY ADVISORS, LLC 360 NORTH CRESCENT DRIVE, SOUTH BUILDING BEVERLY HILLS, CA90210 X Signatures See Exhibit 99.1 - Signatures 04/05/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Two Forms 4 are being filed, covering a total of twelve (12) reporting persons. This is the second of the two Forms 4 (the "Second Form 4"). The first of the two Forms 4 (the "First Form 4") is being filed by each of: (i) PE One Source Holdings, LLC, a Delaware limited liability company ("PE One Source"), (ii) Platinum Equity Capital Partners V, L.P., a Delaware limited partnership ("PECP V"), (iii) Platinum Equity Partners V, L.P., a Delaware limited partnership ("PEP V LP"), (iv) Platinum Equity Partners V, LLC, a Delaware limited liability company ("PEP V LLC"), (v) Platinum Equity Investment Holdings V, LLC, a Delaware limited liability company ("PEIH V"), (vi) Platinum Equity Investment Holdings V Manager, LLC, a Delaware limited liability company ("PEIH V Manager"), (vii) Platinum Equity InvestCo, L.P., a Cayman Islands limited partnership ("PEIC LP"), (viii) Platinum InvestCo (Cayman), LLC, a Cayman Islands limited liability company ("PIC LLC"), ( 2 )(Continued From Footnote 1) (ix) Platinum Equity Investment Holdings IC (Cayman), LLC, a Delaware limited liability company ("PEIH IC LLC"), and (x) Platinum Equity Investment Holdings, LLC, a Delaware limited liability company ("Platinum Holdings"). This Form 4 is being filed by (xi) Platinum Equity, LLC, a Delaware limited liability company ("Platinum Equity," and together with the entities listed in clauses (i)-(x), the "Platinum Entities," and (xii) Tom Gores, an individual and citizen of the United States (each person or entity listed in clauses (i)-(xii), a "Reporting Person" and, collectively, the "Reporting Persons"). PE One Source directly owns 148,600,000 shares of common stock, par value $0.0001 per share (the "Shares"), of Custom Truck One Source, Inc. (the "Issuer"). PECP V holds a majority of the outstanding equity in PE One Source and, accordingly, may be deemed to beneficially own the Shares beneficially owned by PE One Source. ( 3 )(Continued From Footnote 2) PEP V LP is the general partner of PECP V and, accordingly, may be deemed to beneficially own the Shares beneficially owned by PECP V. PEP V LLC is the general partner of PEP V LP and, accordingly, may be deemed to beneficially own the Shares beneficially owned by PEP V LP. PEIH V holds all of the outstanding equity in PEP V LLC and, accordingly, may be deemed to beneficially own the Shares beneficially owned by PEP V LLC. PEIH V Manager is the sole manager of PEIH V and, accordingly, may be deemed to beneficially own the Shares beneficially owned by PEIH V. PEIC LP holds all of the outstanding equity in PEIH V and, accordingly, may be deemed to beneficially own the Shares beneficially owned by PEIH V. PIC LLC holds a controlling interest in PEIC LP and, accordingly, may be deemed to beneficially own the Shares beneficially owned by PEIC LP. PEIH IC LLC is the general partner of PEIC LP and, accordingly, may be deemed to beneficially own the Shares beneficia ( 4 )(Continued From Footnote 3) Platinum Equity is the sole member of Platinum Holdings, and PEIH V Manager and, accordingly, may be deemed to beneficially own the Shares beneficially owned by each of Platinum Holdings and PEIH V Manager. Platinum Equity and Tom Gores, together, hold a controlling interest in PIC LLC and may be deemed to beneficially own the Shares beneficially owned by PIC LLC. Tom Gores is the Chairman and Chief Executive Officer of Platinum Equity and, accordingly, may be deemed to beneficially own the Shares beneficially owned by Platinum Equity. Mr. Gores disclaims beneficial ownership of all the Shares held by each of the entities listed above with respect to which he does not have a pecuniary interest. Because of the relationship discussed above, each Reporting Person may be deemed to beneficially own the Shares reported in this Form 4. ( 5 )Pursuant to Rule 16a-1(a)(4) under the Exchange Act, this filing shall not be deemed an admission that the Reporting Persons are, for purposes of Section 16 of the Exchange Act or otherwise, the beneficial owners of any equity securities in excess of their respective pecuniary interests.

Remarks: PE One Source, which is indirectly controlled by Tom Gores as described in footnotes 1-4, is party to an Amended and Restated Stockholders' Agreement with the Issuer (the "Stockholders' Agreement"), which gives PE One Source the right to nominate up to seven (7) directors to the Issuer's board of directors, subject to certain ownership thresholds. Louis Samson, David Wolf, Bryan Kelln and David Glatt serve on the Issuer's board of directors pursuant to this right. Each of Messrs. Kelln and Samson is a Partner, and each of Messrs. Glatt and Wolf is a Managing Director, of Platinum Equity. Accordingly, Messrs. Kelln, Samson, Glatt and Wolf may be determined to represent the interests of the Platinum Entities and Mr. Gores on the board of directors of the Issuer, and accordingly, the Platinum Entities and Mr. Gores may be deemed to be directors for purposes of Section of the Securities Exchange Act of 1934, as amended.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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