X0306 4 2021-02-11 0 0001664710 Keros Therapeutics, Inc. KROS 0001808322 Lachey Jennifer C/O KEROS THERAPEUTICS, INC. 99 HAYDEN AVENUE, SUITE 120, BUILDING E LEXINGTON MA 02421 0 1 0 0 Chief Scientific Officer Common Stock 2021-02-11 4 M 0 5300 0.30 A 33291 D Common Stock 2021-02-11 4 S 0 447 62.85 D 32844 D Common Stock 2021-02-11 4 S 0 1460 63.74 D 31384 D Common Stock 2021-02-11 4 S 0 1272 64.93 D 30112 D Common Stock 2021-02-11 4 S 0 1845 65.99 D 28267 D Common Stock 2021-02-11 4 S 0 262 67.05 D 28005 D Common Stock 2021-02-11 4 S 0 14 68.05 D 27991 D Employee Stock Option (right to buy) 0.30 2021-02-11 4 M 0 5300 0.00 D 2028-03-25 Common Stock 5300 145605 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 $62.33 to $63.29 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), (5) and (6). The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $63.345 to $64.34 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $64.345 to $65.34 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $65.355 to $66.24 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $66.69 to $67.635 inclusive. Immediately exercisable. /s/ Keith Regnante, Attorney-in-Fact 2021-02-16