Geoff Mcdonough - 15 Jan 2026 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: 15 Jan 2026
Net transactions value: -$773
Form type: 4
Filing time: 16 Jan 2026, 16:05:14 UTC
Previous filing: 21 Nov 2025
Next filing: 04 Feb 2026
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	16 Jan 2026	0001732701

Transactions Table

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Ownership	Footnotes
transaction	GBIO	Common Stock	Options Exercise		+395	+0.29%		137,597	15 Jan 2026	Direct	F1
transaction	GBIO	Common Stock	Tax liability	$773	-137	-0.1%	$5.64	137,460	15 Jan 2026	Direct
holding	GBIO	Common Stock						22,646	15 Jan 2026	By 2018 Trust	F2
holding	GBIO	Common Stock						27,500	15 Jan 2026	By 2020 Trust	F3

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	+395	+33%	$0.000000	1,582	15 Jan 2026	Common Stock	395		Direct	F1, F4

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

Explanation of Responses:

Id	Content
F1	Each restricted stock unit represents the right to receive one share of the company's common stock.
F2	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.
F3	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.
F4	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.