X0306 4 2021-09-01 0 0001496323 IGM Biosciences, Inc. IGMS 0001787362 Keyt Bruce C/O IGM BIOSCIENCES, INC. 325 E. MIDDLEFIELD ROAD MOUNTAIN VIEW CA 94043 0 1 0 0 Chief Scientific Officer Common Stock 2021-09-01 4 M 0 2500 0.93 A 5557 D Common Stock 2021-09-01 4 F 0 1256 71.79 D 4301 D Common Stock 2021-09-03 4 S 0 1244 70.6851 D 3057 D Common Stock 1013 I See footnote Stock Option (right to buy) 0.93 2021-09-01 4 M 0 2500 0.00 D 2025-03-10 Common Stock 2500 5264 D The option exercise and sale were effected pursuant to a Rule 10b5-1 trading plan entered into by the Reporting Person. Represents shares withheld by the Issuer to pay the exercise price and taxes pursuant to the "net exercise" of 2,500 option shares. This transaction was executed in multiple trades at prices ranging from $70.02 to $71.59. The price reported above reflects the weighted average sale price. The Reporting Person undertakes to provide upon request by the staff of the Securities and Exchange Commission, the Issuer, or a security holder of the Issuer, full information regarding the number of shares sold at each separate sale price. The shares are held directly by the reporting person's spouse. The shares subject to the option are vested and exercisable as of the date hereof. /s/ Misbah Tahir, by power of attorney 2021-09-03