Sec Form 4 Filing - ArcLight CTC Holdings, L.P. @ ArcLight Clean Transition Corp. - 2021-06-14

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

OMB APPROVAL OMB Number: 3235-0287 Expires: November 30, 2011 Estimated average burden hours per response... 0.5

1. Name and Address of Reporting Person ArcLight CTC Holdings, L.P. 2. Issuer Name and Ticker or Trading Symbol ArcLight Clean Transition Corp. [ PTRA] 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) 200 CLARENDON ST, 55TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 06/14/2021 (Street) BOSTON, MA02116 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ 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 06/14/2021 C( 2 )( 3 ) 6,797,500 A 6,797,500 D ( 1 ) ( 2 ) ( 3 ) Common Stock 06/14/2021 J( 2 )( 3 ) 428 D 6,797,072 D ( 1 ) ( 2 ) ( 3 )

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 Class B Ordinary Shares ( 2 ) ( 3 ) 06/14/2021 C( 2 )( 3 ) 6,797,500 ( 2 )( 3 ) ( 2 )( 3 ) Common Stock 6,797,500 ( 4 ) ( 2 ) ( 3 ) 0 ( 2 ) ( 3 ) D ( 1 ) ( 2 ) ( 3 ) Warrants ( 4 ) 06/14/2021 J( 4 ) 7,550,000 ( 4 ) ( 4 ) Common Stock 7,550,000 ( 4 ) ( 4 ) 7,550,000 ( 4 ) D ( 1 ) ( 4 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other ArcLight CTC Holdings, L.P. 200 CLARENDON ST, 55TH FLOOR BOSTON, MA02116 X Signatures /s/ ArcLight CTC Holdings, L.P. By: ACTC Holdings GP, LLC, its General Partner /s/ Daniel R. Revers 06/16/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )6,797,072 shares of common stock, par value $0.0001 ("New Proterra Common Stock"), of New Proterra (as defined below) are held directly by ArcLight CTC Holdings, L.P. a Delaware limited liability partnership (the "Sponsor"). Daniel R. Revers has voting and investment discretion with respect to the securities held by the Sponsor, and thus may be deemed to have beneficial ownership of such securities. Mr. Revers expressly disclaims any such beneficial ownership of such securities, except to the extent of his individual pecuniary interests therein. The business address of Sponsor and Mr. Revers is 200 Clarendon Street, 55th Floor, Boston, MA 02116. ( 2 )Pursuant to the Agreement and Plan of Merger, dated January 11, 2021, by and among ArcLight Clean Transition Corp., a Cayman Islands exempted company (the "Company"), Phoenix Merger Sub, Inc., a Delaware corporation, and Proterra Inc, a Delaware corporation ("Proterra"), the parties effected a business combination transaction ("Business Combination") on June 14, 2021. In connection with the Business Combination, the Company domesticated as a Delaware corporation (the "Domestication") and changed its name to "Proterra Inc" ("New Proterra"). In connection with the consummation of the Business Combination, 6,797,500 of Sponsor's Class B ordinary shares, par value $0.0001, of the Company, which were previously convertible into Class A ordinary shares, par value $0.0001, of the Company ("Class A ordinary shares") converted into shares of common stock, par value $0.0001, of New Proterra ("New Proterra Common Stock") simultaneously with the closing of the Business Combination. ( 3 )Continuation of Footnote 2: Sponsor then forfeited and surrendered for no consideration 428 shares of New Proterra Common Stock. After giving effect to this transaction, Sponsor will own less than 10% of the outstanding common stock of New Proterra. ( 4 )In connection with the consummation of the Business Combination, 7,550,000 of the private placement warrants of the Company ("ArcLight Private Placement Warrants") held by Sponsor, which previously entitled Sponsor to purchase one Class A Ordinary Share at a price of $11.50 per whole share at any time commencing on the later of one year from the closing of the Company's initial public offering or 30 days after the completion of an initial business combination of the Company, were converted into private placement warrants of Proterra (each a "New Proterra Private Placement Warrant") simultaneously with the closing of the Business Combination, with each whole New Proterra Private Placement Warrant entitling the holder thereof to the right to purchase one share of New Proterra Common Stock.

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).

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.