[Form 4] Generation Bio Co. Insider Trading Activity

Rhea-AI Filing Summary

Generation Bio (GBIO) reported an insider transaction by its Chief Legal Officer on October 15, 2025. The officer settled 334 shares of common stock upon the vesting/settlement of restricted stock units (code M). To cover taxes, 99 shares were withheld at $6.71 (code F).

Following these transactions, the officer directly owned 2,345 shares of common stock and held 2,008 restricted stock units. The filing notes amounts reflect the one-for-10 reverse stock split effected on July 21, 2025. The underlying RSU grant was 5,355 units from April 5, 2023, vesting 25% on April 15, 2024, with the remainder vesting in equal quarterly installments thereafter.

SEC Form 4

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
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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).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Howze Yalonda

(Last) (First) (Middle)

C/O GENERATION BIO CO.

301 BINNEY STREET, SUITE 401

(Street)

CAMBRIDGE MA 02142

(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		10% Owner
X	Officer (give title below)		Other (specify below)
	CHIEF LEGAL OFFICER

3. Date of Earliest Transaction (Month/Day/Year)
10/15/2025

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

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	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)
			Code	V	Amount	(A) or (D)	Price
Common Stock	10/15/2025		M		334(1)	A	(2)	2,444(1)	D
Common Stock	10/15/2025		F		99(1)	D	$6.71	2,345(1)	D

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)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Restricted Stock Units	(2)	10/15/2025		M			334	(3)	(3)	Common Stock	334(1)	$0	2,008(1)	D

Explanation of Responses:

1. Amounts reported in this Form 4 reflect the one-for-10 reverse stock split effected by the issuer on July 21, 2025.

2. Each restricted stock unit represents the right to receive one share of the company's common stock.

3. The grant of 5,355 restricted stock units was made on April 5, 2023. The shares underlying the restricted stock units vest over four years, with 25% of the shares vested on April 15, 2024 and the remaining shares vesting in equal quarterly installments thereafter.

	/s/ Shawna-Gay White, Attorney-in-Fact	10/17/2025
	** 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.

FAQ

What did GBIO's insider report on the Form 4?

On October 15, 2025, the Chief Legal Officer settled 334 shares from RSUs and had 99 shares withheld at $6.71 for taxes.

How many GBIO shares does the reporting person own after the transaction?

Direct ownership is 2,345 shares of common stock after the reported transactions.

How many RSUs does the GBIO insider still hold?

The insider holds 2,008 restricted stock units following the settlement.

What price was used for GBIO share withholding for taxes?

The filing shows tax withholding of 99 shares at $6.71 per share.

Did a stock split affect the reported GBIO amounts?

Yes. Amounts reflect the one-for-10 reverse stock split effected on July 21, 2025.

When were the RSUs originally granted and how do they vest?

Granted on April 5, 2023; 25% vested on April 15, 2024, with the remainder vesting in equal quarterly installments thereafter.