X0306 4 2021-06-01 0 0001664710 Keros Therapeutics, Inc. KROS 0001808365 Knowles Julius C/O KEROS THERAPEUTICS, INC. 99 HAYDEN AVENUE, SUITE 120, BUILDING E LEXINGTON MA 02421 1 0 0 0 Stock Option (right to buy) 51.48 2021-06-01 4 A 0 8293 0.00 A 2031-05-31 Common Stock 8293 8293 D The option shall vest in equal quarterly installments over the 12 months following the date of grant, provided that the grant will in any case be fully vested on the date of Issuer's 2022 annual meeting of stockholders, subject to the Reporting Person continuing to provide service through each such date. /s/ Keith Regnante, Attorney-in-Fact 2021-06-03