GBIO Generation Bio Company

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 OF SECURITIES                                                                                   
OMB APPROVAL
OMB Number: 3235-0287
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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940                       

1. Name and Address of Reporting Person * Atlas Venture Fund X, L.P.	2. Issuer Name and Ticker or Trading Symbol Generation Bio Co. [ GBIO ]	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) 300 TECHNOLOGY SQUARE, 8TH FLOOR	3. Date of Earliest Transaction (MM/DD/YYYY) 6/16/2021
(Street) CAMBRIDGE, MA 02139 (City)        (State)        (Zip)	4. If Amendment, Date Original Filed (MM/DD/YYYY)	6. Individual or Joint/Group Filing (Check Applicable Line) ___ Form filed by One Reporting Person _ X _ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security (Instr. 3)	2. Trans. Date	2A. Deemed Execution Date, if any	3. Trans. 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	6/16/2021		J(1)		1000000	D	$0.00	8111939	D
Common Stock	6/16/2021		J(2)		100000	D	$0.00	1266937	I	See footnote (3)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Trans. Date	3A. Deemed Execution Date, if any	4. Trans. 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		7. Title and Amount of Securities Underlying Derivative Security (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

Explanation of Responses:
(1)	Represents a pro rata distribution, and not a purchase or sale of securities, by Atlas Venture Fund X, L.P. ("Atlas Venture Fund X") to its general partner and limited partners without additional consideration. This distribution was effected pursuant to a plan adopted by Atlas Venture Fund X pursuant to Rule 10b5-1 on April 20, 2021.
(2)	Represents a pro rata distribution, and not a purchase or sale of securities, by Atlas Venture Opportunity Fund I, LP ("AVOF I") to its general partner and limited partners without additional consideration. This distribution was effected pursuant to a plan adopted by AVOF I pursuant to Rule 10b5-1 on April 20, 2021.
(3)	The shares are owned directly by AVOF I.

Reporting Owners
Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Atlas Venture Fund X, L.P. 300 TECHNOLOGY SQUARE, 8TH FLOOR CAMBRIDGE, MA 02139		X
Atlas Venture Opportunity Fund I, L.P. 300 TECHNOLOGY SQUARE, 8TH FLOOR CAMBRIDGE, MA 02139		X

Signatures
Atlas Venture Fund X, LP, By: Atlas Venture Associates X, L.P., its general partner, By: Atlas Venture Associates X, LLC, its general partner, By: /s/ Ommer Chohan, Chief Financial Officer		6/21/2021
**Signature of Reporting Person		Date
Atlas Venture Opportunity Fund I, L.P., By: Atlas Venture Associates Opportunity I, L.P., its general partner, By: Atlas Venture Associates Opportunity I, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan		6/21/2021
**Signature of Reporting Person		Date