X0306 4 2021-03-01 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 Common Stock 2021-03-01 4 S 0 1608 61.33 D 657219 I See footnote Common Stock 2021-03-01 4 S 0 1050 61.33 D 438584 I See footnote Common Stock 2021-03-01 4 S 0 2257 62.11 D 654962 I See footnote Common Stock 2021-03-01 4 S 0 1473 62.11 D 437111 I See footnote Common Stock 2021-03-01 4 S 0 1794 63.22 D 653168 I See footnote Common Stock 2021-03-01 4 S 0 1169 63.22 D 435942 I See footnote Common Stock 2021-03-01 4 S 0 625 64.09 D 652543 I See footnote Common Stock 2021-03-01 4 S 0 406 64.09 D 435536 I See footnote Common Stock 2021-03-01 4 S 0 734 65.29 D 651809 I See footnote Common Stock 2021-03-01 4 S 0 479 65.28 D 435057 I See footnote Common Stock 2021-03-01 4 S 0 792 66.04 D 651017 I See footnote Common Stock 2021-03-01 4 S 0 516 66.04 D 434541 I See footnote Common Stock 2021-03-01 4 S 0 46 67.60 D 650971 I See footnote Common Stock 2021-03-01 4 S 0 30 67.60 D 434511 I See footnote Common Stock 2021-03-02 4 S 0 3644 57.93 D 647327 I See footnote Common Stock 2021-03-02 4 S 0 2377 57.93 D 432134 I See footnote Common Stock 2021-03-02 4 S 0 1095 58.90 D 646232 I See footnote Common Stock 2021-03-02 4 S 0 714 58.90 D 431420 I See footnote Common Stock 2021-03-02 4 S 0 1052 60.05 D 645180 I See footnote Common Stock 2021-03-02 4 S 0 686 60.05 D 430734 I See footnote Common Stock 2021-03-02 4 S 0 554 60.61 D 644626 I See footnote Common Stock 2021-03-02 4 S 0 361 60.61 D 430373 I See footnote Common Stock 2021-03-02 4 S 0 138 61.90 D 644488 I See footnote Common Stock 2021-03-02 4 S 0 90 61.90 D 430283 I See footnote 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 $60.63 to $61.62 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), (5), (6), (7), (8), (9), (10), (11), (12), (13) and (14). The securities are held by Partners Innovation Fund, LLC ("PIF I"). Partners Innovation Fund, LLC ("Partners GP I") is the ultimate general partner of PIF I. The Reporting Person, a member of the board of directors of the Issuer, is a partner of Partners GP I and as a result, may be deemed to share voting and investment power with respect to the shares held by PIF I. The securities are held by Partners Innovation Fund II, L.P. ("PIF II"). Partners Innovation Fund II, LLC ("Partners GP II") is the ultimate general partner of PIF II. The Reporting Person, a member of the board of directors of the Issuer, is a partner of Partners GP II and as a result, may be deemed to share voting and investment power with respect to the shares held by PIF II. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $61.66 to $62.65 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $62.67 to $63.65 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $63.70 to $64.52 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $64.73 to $65.66 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $65.77 to $66.50 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $57.38 to $58.36 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $58.39 to $59.37 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $59.42 to $60.40 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $60.42 to $61.00 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $61.70 to $62.00 inclusive. /s/ Keith Regnante, Attorney-in-Fact 2021-03-03