Sec Form 4 Filing - Porter Brook F @ 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

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1. Name and Address of Reporting Person Porter Brook F 2. Issuer Name and Ticker or Trading Symbol ArcLight Clean Transition Corp. [ PTRA] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O PROTERRA INC, 1815 ROLLINS ROAD 3. Date of Earliest Transaction (MM/DD/YY) 06/14/2021 (Street) BURLINGAME, CA94010 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 A( 1 ) 1,000,000 A 1,000,000 I See Footnote ( 2 ) Common Stock 06/14/2021 A( 3 ) 1,532,233 A 2,532,233 I See Footnote ( 2 )

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 Employee Stock Option (Right to Buy) $ 4.98 06/14/2021 A 200,812 ( 4 ) 09/25/2028 Common Stock 200,812 ( 3 ) 200,812 D Employee Stock Option (Right to Buy) $ 6 06/14/2021 A 44,625 ( 5 ) 12/22/2029 Common Stock 44,625 ( 3 ) 44,625 D Employee Stock Option (Right to Buy) $ 4.78 06/14/2021 A 20,081 ( 6 ) 12/20/2030 Common Stock 20,081 ( 3 ) 20,081 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Porter Brook F C/O PROTERRA INC 1815 ROLLINS ROAD BURLINGAME, CA94010 X Signatures /s/ Joshua Damm, Attorney-in-Fact 06/16/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )In connection with the closing of the business combination (the "Business Combination") of ArcLight Clean Transition Corp. ("ArcLight") and Proterra Inc ("Old Proterra"), G2VP I, LLC acquired shares of the Issuer's common stock at a price of $10.00 per share on the terms and conditions set forth in a subscription agreement. ( 2 )G2VP I, LLC, for itself and as nominee for G2VP Founders Fund I, LLC, is the record holder of the securities reported herein. The Reporting Person, together with Ben Kortlang, David Mount and Daniel Oros, is a managing member of G2VP I Associates, LLC, which is the managing member of G2VP, and may be deemed to share voting and dispositive control over the shares held by G2VP. G2VP I Associates, LLC and each of its managing members disclaim beneficial ownership of these shares held by G2VP except to the extent of any pecuniary interest therein. ( 3 )Pursuant to the Business Combination, each share of Old Proterra outstanding common stock was automatically converted into the right to receive shares of the Issuer's Common Stock based on a 1 to 0.8925 conversion ratio ("Conversion Ratio"). In addition, each outstanding Old Proterra equity award was automatically converted into a corresponding equity award of the Issuer based on the Conversion Ratio and with the same terms and vesting conditions as the Old Proterra equity award. ( 4 )The stock option vests as of 1/48 of the total shares monthly beginning on October 25, 2018 until fully vested, subject to the Reporting Person's provision of service to the Issuer on each vesting date. ( 5 )The stock option vests as of 1/48 of the total shares monthly beginning on January 23, 2020 until fully vested, subject to the Reporting Person's provision of service to the Issuer on each vesting date. ( 6 )The stock option vests as of 1/48 of the total shares monthly beginning on January 21, 2021 until fully vested, subject to the Reporting Person's provision of service to the Issuer on each vesting date.

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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