Form 4 Generation Bio Co. For: Jun 21 Filed by: ATLAS VENTURE ASSOCIATES X, L.P.

June 23, 2021 8:27 PM EDT

FORM 4

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
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:		3235-0287
Expires:	December 31, 2014
Estimated average burden
hours per response:		0.5

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

1. Name and Address of Reporting Person ^*

ATLAS VENTURE ASSOCIATES X, L.P.

(Last)

(First)

(Middle)

300 TECHNOLOGY SQUARE, 8TH FLOOR

(Street)

CAMBRIDGE

02139

(City)

(State)

(Zip)

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)

3. Date of Earliest Transaction (Month/Day/Year)
06/21/2021

4. If Amendment, Date of Original Filed (Month/Day/Year)

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. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	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)
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	Code	V	Amount	(A) or (D)	Price		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
Common Stock	06/21/2021		S⁽¹⁾		59,978 ⁽²⁾	D	$ 24.82 ⁽³⁾	155,708 ⁽²⁾	D ⁽⁴⁾
Common Stock	06/21/2021		S⁽¹⁾		3,796 ⁽²⁾	D	$ 25.12 ⁽⁵⁾	151,912 ⁽²⁾	D ⁽⁴⁾
Common Stock	06/21/2021		S⁽¹⁾		111 ⁽⁶⁾	D	$ 24.82 ⁽³⁾	897 ⁽⁶⁾	I	See footnote ⁽⁷⁾
Common Stock	06/21/2021		S⁽¹⁾		7 ⁽⁶⁾	D	$ 25.12 ⁽⁵⁾	890 ⁽⁶⁾	I	See footnote ⁽⁷⁾
Common Stock	06/22/2021		S⁽¹⁾		33,261 ⁽²⁾	D	$ 24.76 ⁽⁸⁾	118,651 ⁽²⁾	D ⁽⁴⁾
Common Stock	06/22/2021		S⁽¹⁾		25,208 ⁽²⁾	D	$ 25.2 ⁽⁹⁾	93,443 ⁽²⁾	D ⁽⁴⁾
Common Stock	06/22/2021		S⁽¹⁾		61 ⁽⁶⁾	D	$ 24.76 ⁽⁸⁾	829 ⁽⁶⁾	I	See footnote ⁽⁷⁾
Common Stock	06/22/2021		S⁽¹⁾		47 ⁽⁶⁾	D	$ 25.2 ⁽⁹⁾	782 ⁽⁶⁾	I	See footnote ⁽⁷⁾
Common Stock	06/23/2021		S⁽¹⁾		34,162 ⁽²⁾	D	$ 25.08 ⁽¹⁰⁾	59,281 ⁽²⁾	D ⁽⁴⁾
Common Stock	06/23/2021		S⁽¹⁾		28,331 ⁽²⁾	D	$ 25.69 ⁽¹¹⁾	30,950 ⁽²⁾	D ⁽⁴⁾
Common Stock	06/23/2021		S⁽¹⁾		63 ⁽⁶⁾	D	$ 25.08 ⁽¹⁰⁾	719 ⁽⁶⁾	I	See footnote ⁽⁷⁾
Common Stock	06/23/2021		S⁽¹⁾		53 ⁽⁶⁾	D	$ 25.69 ⁽¹¹⁾	666 ⁽⁶⁾	I	See footnote ⁽⁷⁾

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 (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	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 (Month/Day/Year)		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: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	8. Price of Derivative Security (Instr. 5)		10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)

Explanation of Responses:

1. Shares were sold pursuant to a Rule 10b5-1 trading plan dated April 20 ,2021.

2. The shares reported herein give effect to the pro rata distribution of shares by Atlas Venture Fund X, L.P. for no additional consideration to its limited partners and its and general partner, Atlas Venture Associates X, L.P. ("AVA X LP"), subsequent to the Reporting Persons' last Section 16 filing reporting ownership of the Issuer's Common Stock. As the distribution of such shares constituted only a change in the form of the Reporting Persons' ownership in such shares, the Reporting Persons were not required to report the distribution pursuant to Section 16.

3. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $24.08 to $25.07 inclusive. The Reporting Persons undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in footnotes (3), (5), (8), (9), (10) and (11).

4. The shares are held directly by AVA X LP. Atlas Venture Associates X, LLC ("AVA X LLC") is the general partner of AVA X LP. AVA X LLC disclaims Section 16 beneficial ownership of the securities held by AVA X LP except to the extent of its pecuniary interest therein, if any.

5. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $25.08 to $25.20 inclusive.

6. The shares reported herein give effect to the pro rata distribution of shares by Atlas Venture Opportunity Fund I, L.P. for no additional consideration to its limited partners and its and general partner, Atlas Venture Associates Opportunity I, LP ("AVAO LP"), subsequent to the Reporting Persons' last Section 16 filing reporting ownership of the Issuer's Common Stock. As the distribution of such shares constituted only a change in the form of the Reporting Persons' ownership in such shares, the Reporting Persons were not required to report the distribution pursuant to Section 16.

7. The shares are held directly by AVAO LP. Atlas Venture Associates Opportunity I, LLC ("AVAO LLC") is the general partner of AVAO LP. AVAO LLC disclaims Section 16 beneficial ownership of the securities held by AVAO LP except to the extent of its pecuniary interest therein, if any.

8. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $24.08 to $25.07 inclusive.

9. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $25.10 to $25.285 inclusive.

10. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $24.63 to $25.62 inclusive.

11. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $25.63 to $25.95 inclusive.

	Atlas Venture Associates X, L.P., By: Atlas Venture Associates X, LLC, Its: General Partner, By: /s/ Ommer Chohan, Chief Financial Officer	06/23/2021
	** Signature of Reporting Person	Date
	Atlas Venture Associates X, LLC, By: /s/ Ommer Chohan, Chief Financial Officer	06/23/2021
	** Signature of Reporting Person	Date
	Atlas Venture Associates Opportunity I, L.P., By: Atlas Venture Associates Opportunity I, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan	06/23/2021
	** Signature of Reporting Person	Date
	Atlas Venture Associates Opportunity I, LLC, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan	06/23/2021
	** Signature of Reporting Person	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).
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.

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Form 4 Generation Bio Co. For: Jun 21 Filed by: ATLAS VENTURE ASSOCIATES X, L.P.

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