GEOFF MCDONOUGH - 31 Oct 2025 Form 4 Insider Report for Generation Bio Co. (GBIO)

Role: Director
Signature: /s/ Shawna-Gay White, Attorney-in-Fact
Issuer symbol: GBIO
Transactions as of: 31 Oct 2025
Net transactions value: -$1,614
Form type: 4
Filing time: 21 Nov 2025, 17:00:11 UTC
Previous filing: 17 Oct 2025
SEC: View on sec.gov

Reporting Owners (1)

Name	Relationship	Address	Signature	Signature date	CIK
MCDONOUGH GEOFF	Director	C/O GENERATION BIO CO., 301 BINNEY ST, CAMBRIDGE	/s/ Shawna-Gay White, Attorney-in-Fact	21 Nov 2025	0001732701

Transactions Table

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Ownership	Footnotes
transaction	GBIO	Common Stock	Options Exercise		+659	+0.48%		137,495	31 Oct 2025	Direct	F1, F2
transaction	GBIO	Common Stock	Tax liability	$1,614	-293	-0.21%	$5.51	137,202	31 Oct 2025	Direct
holding	GBIO	Common Stock						22,646	31 Oct 2025	By 2018 Trust	F3
holding	GBIO	Common Stock						27,500	31 Oct 2025	By 2020 Trust	F4

Derivative Securities (e.g., puts, calls, warrants, options, convertible securities)

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Underlying Class	Amount	Exercise Price	Ownership	Footnotes
transaction	GBIO	Restricted Stock Units	Options Exercise	$0	-659	-25%	$0.000000	1,977	31 Oct 2025	Common Stock	527		Direct	F1, F2, F5

* An asterisk sign (*) next to the price indicates that the price is likely invalid.

Explanation of Responses:

Id	Content
F1	Reflects an acceleration of vesting due to the reporting person's resignation as the Issuer's Chief Executive Officer & President.
F2	Each restricted stock unit represents the right to receive one share of the company's common stock.
F3	The securities are directly held by the McDonough Family 2018 Irrevocable Trust, or the 2018 Trust. The reporting person is the settlor of the 2018 Trust, Allison L. McDonough and David S. Grayzel are trustees for the 2018 Trust, and the 2018 Trust is for the benefit of Graeme and Owen McDonough. The reporting person may be deemed to beneficially own the shares of common stock owned by the 2018 Trust.
F4	The securities are directly held by the McDonough Family 2020 Irrevocable Trust, or the 2020 Trust. The reporting person is the settlor of the 2020 Trust, Allison L. McDonough and David S. Grayzel are trustees for the 2020 Trust, and the 2020 Trust is for the benefit of Allison, Graeme and Owen McDonough. The reporting person may be deemed to beneficially own the shares of common stock owned by the 2020 Trust.
F5	On January 20, 2023, the reporting person was granted 8,437 restricted stock units. The shares underlying the restricted stock units vest over two years, with 25% of the shares vesting on July 15, 2022 and the remaining shares vesting in equal quarterly installments thereafter.