X0306 4 2021-04-14 0 0001662579 C4 Therapeutics, Inc. CCCC 0001824862 Anderson Kenneth Carl C/O C4 THERAPEUTICS, INC. 490 ARSENAL WAY #200 WATERTOWN MA 02472 1 0 0 0 Common Stock 2021-04-13 5 G 0 E 2278 0.00 A 84435 D Common Stock 2021-04-13 5 G 0 E 2278 0.00 A 47316 I By Spouse Common Stock 2021-04-14 4 M 0 267 2.11 A 84702 D Common Stock 2021-04-14 4 M 0 444 4.98 A 85146 D Common Stock 61265 I By Kenneth C. Anderson 2016 Grantor Retained Annuity Trust Common Stock 61265 I By Cynthia E. Anderson 2016 Grantor Retained Annuity Trust Common Stock 16939 I By Kenneth C. Anderson 2015 Irrevocable Trust Common Stock 16939 I By Cynthia E. Anderson 2015 Irrevocable Trust Stock Option (Right to Buy) 2.11 2021-04-14 4 M 0 267 0.00 D 2026-07-12 Common Stock 267 2940 D Stock Option (Right to Buy) 4.98 2021-04-14 4 M 0 444 0.00 D 2030-07-02 Common Stock 444 4002 D On April 13, 2021, Kenneth C. Anderson received a distribution of 2,278 shares of the Issuer's common stock from the Kenneth C. Anderson 2016 Grantor Retained Annuity Trust. On April 13, 2021, Cynthia E. Anderson received a distribution of 2,278 shares of the Issuer's common stock from the Cynthia E. Anderson 2016 Grantor Retained Annuity Trust. Shares held by the Kenneth C. Anderson 2016 Grantor Retained Annuity Trust. The Reporting Person disclaims beneficial ownership of these shares except to the extent of his pecuniary interest therein. Shares held the Cynthia E. Anderson 2016 Grantor Retained Annuity Trust. The Reporting Person disclaims beneficial ownership of these shares except to the extent of his pecuniary interest therein. Shares held by the Kenneth C. Anderson 2015 Irrevocable Trust. The Reporting Person disclaims beneficial ownership of these shares except to the extent of his pecuniary interest therein. Shares held by the Cynthia E. Anderson 2015 Irrevocable Trust. The Reporting Person disclaims beneficial ownership of these shares except to the extent of his pecuniary interest therein. Represents underlying unexercised stock options that were granted on July 13, 2016. The terms of the original grant provide that 12.5% of this option vested and became exercisable on December 31, 2016, with the remainder vesting in 28 equal quarterly installments thereafter. Represents underlying unexercised options that were granted on July 3, 2020. The terms of the original grant provide that this option shall vest and become exercisable in 12 equal quarterly installments, with the first installment vested on October 1, 2020. /s/ Jolie M. Siegel, Attorney-in-Fact 2021-04-14