X0306 4 2021-02-11 0 0001664710 Keros Therapeutics, Inc. KROS 0001808290 Ordonez Claudia C/O KEROS THERAPEUTICS, INC. 99 HAYDEN AVENUE, SUITE 120, BUILDING E LEXINGTON MA 02421 0 1 0 0 Chief Medical Officer Common Stock 2021-02-11 4 M 0 1000 0.48 A 1000 D Common Stock 2021-02-11 4 S 0 175 63.10 D 825 D Common Stock 2021-02-11 4 S 0 312 64.17 D 513 D Common Stock 2021-02-11 4 S 0 216 65.35 D 297 D Common Stock 2021-02-11 4 S 0 295 66.19 D 2 D Common Stock 2021-02-11 4 S 0 2 68.05 D 0 D Employee Stock Option (right to buy) 0.48 2021-02-11 4 M 0 1000 0.00 D 2029-09-18 Common Stock 1000 102211 D The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 trading plan. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $62.71 to $63.51 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 sold at each separate price within the ranges set forth in footnotes (2), (3), (4) and (5). The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $63.775 to $64.535 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $64.855 to $65.73 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $66.00 to $66.69 inclusive. One-quarter (1/4th) of the shares subject to the option shall vest on September 16, 2020, and one-twelfth (1/12th) of the remaining shares subject to the option shall vest in equal quarterly installments thereafter, subject to the Reporting Person continuing to provide service through each such date. /s/ Keith Regnante, Attorney-in-Fact 2021-02-16