X0306 4 2021-12-15 0 0001662244 Cyteir Therapeutics, Inc. CYT 0001331852 Zakrzewski Joseph S 128 SPRING ST, BUILDING A, SUITE 510 LEXINGTON MA 02421 1 0 0 0 Common Stock 2021-12-15 4 P 0 2000 10.47 A 79267 D Common Stock 2021-12-15 4 P 0 1700 11.12 A 80967 D Common Stock 58671 I See Footnote Common Stock 149051 I See Footnote The price reported is a weighted average price. These shares were purchased in multiple transactions ranging from $9.95 to $10.88, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the range. 84,523 of the shares of common stock held directly and indirectly by the Reporting Person were acquired upon early exercise of an option and are subject to forfeiture until they vest. The price reported is a weighted average price. These shares were purchased in multiple transactions ranging from $10.95 to $11.61, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the range. Shares held by Z Investments, LLC, of which the Reporting Person is the Managing Director. The Reporting Person disclaims beneficial ownership of the securities reported herein, except to the extent of his pecuniary interest therein. Shares held by Z3 Trust, of which the Reporting Person is a Trustee. The Reporting Person disclaims beneficial ownership of the securities reported herein, except to the extent of his pecuniary interest therein. /s/ Andrew Gengos, Attorney-in-Fact 2021-12-15