X0306 4 2020-06-11 0 0001733294 Generation Bio Co. GBIO 0001577014 Rhodes Jason P C/O GENERATION BIO CO., 301 BINNEY STREET CAMBRIDGE MA 02142 1 0 0 0 Stock Option (right to buy) 19.00 2020-06-11 4 A 0 52000 0.00 A 2030-06-10 Common Stock 52000 52000 D This option was granted on June 11, 2020. The shares underlying the option vest over four years, with 25% of the shares vesting on June 11, 2021 and the remaining shares vesting in equal quarterly installments thereafter. This option was granted to the Reporting Person, a director of the Issuer. The proceeds of any sale of shares of common stock issued to the Reporting Person upon exercise of this option will be transferred to Atlas Venture Life Science Advisors, LLC and as such, the Reporting Person disclaims ownership of such securities reported herein for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, except to the extent of his pecuniary interest therein, if any. /s/ Ommer Chohan, Attorney-in-Fact 2020-06-15