X0306 4 2021-04-21 0 0001745999 Beam Therapeutics Inc. BEAM 0001786304 Evans John M. C/O BEAM THERAPEUTICS INC. 26 LANDSDOWNE STREET CAMBRIDGE MA 02139 1 1 0 0 CEO Common Stock 2021-04-21 4 S 0 1463 67.90 D 1038966 D Common Stock 2021-04-21 4 S 0 5079 69.02 D 1033887 D Common Stock 2021-04-21 4 S 0 5595 70.23 D 1028292 D Common Stock 2021-04-21 4 S 0 9869 71.38 D 1018423 D Common Stock 2021-04-21 4 S 0 2994 71.79 D 1015429 D Common Stock 2021-04-23 4 M 0 6000 1.03 A 1021429 D Common Stock 223000 I By John M. Evans, III 2018 Irrevocable Trust Stock Option (Right to Buy) 1.03 2021-04-23 4 M 0 6000 0.00 D 2028-07-13 Common Stock 6000 396345 D The reported transactions were effected pursuant to a Rule 10b5-1 trading plan. Each price reported for transactions affected pursuant to the Rule 10b5-1 trading plan is a weighted average price. The Reporting Person undertakes to provide to BEAM, any security holder of BEAM 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 range. These shares were sold in multiple transactions ranging from $67.67 to $68.00 inclusive. These shares were sold in multiple transactions ranging from $68.67 to $69.55 inclusive. These shares were sold in multiple transactions ranging from $69.68 to $70.68 inclusive. These shares were sold in multiple transactions ranging from $70.68 to $71.66 inclusive. These shares were sold in multiple transactions ranging from $71.68 to $71.92 inclusive. The option vests as to 25% on the first anniversary of the of the vesting commencement date, January 8, 2018, and at a rate of 2.78% each month thereafter until the option is fully vested. By: /s/ Christine Bellon, Attorney-in-fact 2021-04-23