Sec Form 3 Filing - Samayoa Phillip @ Generation Bio Co. - 2022-09-16

FORM 3 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 Samayoa Phillip 2. Issuer Name and Ticker or Trading Symbol Generation Bio Co. [ GBIO] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) CHIEF STRATEGY OFFICER (Last) (First) (Middle) C/O GENERATION BIO CO., 301 BINNEY STREET, SUITE 401 3. Date of Earliest Transaction (MM/DD/YY) 09/16/2022 (Street) CAMBRIDGE, MA02142 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 92,905 D

Stock Option (right to buy) 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 Stock Option (right to buy) $ 4.5924 ( 1 ) 04/01/2028 Common Stock 6,750 D $ 5.1576 ( 2 ) 03/04/2030 Common Stock 21,406 D Stock Option (right to buy) $ 5.1576 ( 3 ) 03/04/2030 Common Stock 31,138 D Stock Option (right to buy) $ 30.25 ( 4 ) 01/21/2031 Common Stock 22,000 D Stock Option (right to buy) $ 29.38 ( 5 ) 03/31/2031 Common Stock 5,500 D Stock Option (right to buy) $ 35.66 ( 6 ) 05/02/2031 Common Stock 30,000 D Stock Option (right to buy) $ 6.49 ( 7 ) 01/20/2032 Common Stock 58,706 D Restricted Stock Units ( 9 ) ( 8 ) ( 8 ) Common Stock 24,750 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Samayoa Phillip C/O GENERATION BIO CO. 301 BINNEY STREET, SUITE 401 CAMBRIDGE, MA02142 CHIEF STRATEGY OFFICER Signatures /s/ Benjamin Waters, Attorney-in-Fact 09/20/2022 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The option to purchase 36,007 shares was granted on April 2, 2018. The shares underlying the option vest over four years, with 25% of the shares vested on April 2, 2019 and the remaining shares vesting in equal quarterly installments thereafter. ( 2 )The option to purchase 31,138 shares was granted on March 5, 2020. The shares underlying the option vest over four years, with 25% of the shares vested on March 5, 2021 and the remaining shares vesting in equal quarterly installments thereafter. ( 3 )The option to purchase 31,138 shares was granted on March 5, 2020. The shares underlying the option vest in full upon the date on which the Board of Directors of the Issuer determines that the Issuer has dosed the initial patient in its first clinical trial, provided that such event occurs on or before July 1, 2023. ( 4 )The option to purchase 22,000 shares was granted on January 22, 2021. The shares underlying the option vest over four years, with 25% of the shares vested on January 22, 2022 and the remaining shares vesting in equal quarterly installments thereafter. ( 5 )The option to purchase 5,500 shares was granted on April 1, 2021. The shares underlying the option vest over two years, with 25% of the shares vested on October 1, 2021 and the remaining shares vesting in equal quarterly installments thereafter. ( 6 )The option to purchase 30,000 shares was granted on May 3, 2021. The shares underlying the option vest over four years, with 25% of the shares vested on May 3, 2022 and the remaining shares vesting in equal quarterly installments thereafter. ( 7 )The option to purchase 58,706 shares was granted on January 21, 2022. The shares underlying the option vest over four years, with 25% of the shares vesting on January 21, 2023 and the remaining shares vesting in equal quarterly installments thereafter. ( 8 )The grant of 33,000 restricted stock units was made on January 21, 2022. The shares underlying the restricted stock units vest over two years, with 25% of the shares vested on July 15, 2022 and the remaining shares vesting in equal quarterly installments thereafter. ( 9 )Each restricted stock unit represents the right to receive one share of the company's 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).

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