X0306 4 2021-01-04 0 0001745999 Beam Therapeutics Inc. BEAM 0001786484 Burrell Terry-Ann C/O BEAM THERAPEUTICS INC. 26 LANDSDOWNE STREET CAMBRIDGE MA 02139 0 1 0 0 CFO Common Stock 2021-01-04 4 M 0 25000 13.68 A 32309 D Common Stock 2021-01-04 4 S 0 800 78.05 D 31509 D Common Stock 2021-01-04 4 S 0 1951 79.21 D 29558 D Common Stock 2021-01-04 4 S 0 2449 80.25 D 27109 D Common Stock 2021-01-04 4 S 0 6509 81.26 D 20600 D Common Stock 2021-01-04 4 S 0 5296 82.44 D 15304 D Common Stock 2021-01-04 4 S 0 7095 83.15 D 8209 D Common Stock 2021-01-04 4 S 0 900 83.89 D 7309 D Stock Option (Right to Buy) 13.68 2021-01-04 4 M 0 25000 0.00 D 2029-08-31 Common Stock 25000 357941 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. 25% of the shares subject to the stock option vested on the first anniversary of the of the vesting commencement date, August 20, 2019, and the remaining shares shall vest in 36 substantially equal monthly installments thereafter, subject to continued service with BEAM through such dates. These shares were sold in multiple transactions ranging from $77.65 to $78.48 inclusive. These shares were sold in multiple transactions ranging from $78.72 to $79.65 inclusive. These shares were sold in multiple transactions ranging from $79.73 to $80.72 inclusive. These shares were sold in multiple transactions ranging from $80.73 to $81.72 inclusive. These shares were sold in multiple transactions ranging from $81.80 to $82.79 inclusive. These shares were sold in multiple transactions ranging from $82.80 to $83.78 inclusive. These shares were sold in multiple transactions ranging from $83.85 to $84.01 inclusive. By: /s/ Christine Bellon, Attorney-in-fact 2021-01-05