X0306 4 2021-02-16 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 2021-02-16 4 S 0 667 58.48 D 675481 I See footnote Common Stock 2021-02-16 4 S 0 434 58.48 D 450496 I See footnote Common Stock 2021-02-16 4 S 0 1014 59.34 D 674467 I See footnote Common Stock 2021-02-16 4 S 0 661 59.34 D 449835 I See footnote Common Stock 2021-02-16 4 S 0 3999 60.23 D 670468 I See footnote Common Stock 2021-02-16 4 S 0 2609 60.23 D 447226 I See footnote Common Stock 2021-02-16 4 S 0 138 60.92 D 670330 I See footnote Common Stock 2021-02-16 4 S 0 90 60.92 D 447136 I See footnote Common Stock 2021-02-17 4 S 0 645 58.74 D 669685 I See footnote Common Stock 2021-02-17 4 S 0 421 58.74 D 446715 I See footnote Common Stock 2021-02-17 4 S 0 3449 59.96 D 666236 I See footnote Common Stock 2021-02-17 4 S 0 2249 59.96 D 444466 I See footnote Common Stock 2021-02-17 4 S 0 1173 60.66 D 665063 I See footnote Common Stock 2021-02-17 4 S 0 764 60.66 D 443702 I See footnote Common Stock 2021-02-17 4 S 0 1841 61.80 D 663222 I See footnote Common Stock 2021-02-17 4 S 0 1201 61.80 D 442501 I See footnote Common Stock 2021-02-17 4 S 0 2613 62.72 D 660609 I See footnote Common Stock 2021-02-17 4 S 0 1705 62.72 D 440796 I See footnote Common Stock 2021-02-18 4 S 0 230 60.06 D 660379 I See footnote Common Stock 2021-02-18 4 S 0 150 60.06 D 440646 I See footnote Common Stock 2021-02-18 4 S 0 276 61.68 D 660103 I See footnote Common Stock 2021-02-18 4 S 0 180 61.68 D 440466 I See footnote Common Stock 2021-02-18 4 S 0 315 63.04 D 659788 I See footnote Common Stock 2021-02-18 4 S 0 205 63.04 D 440261 I See footnote Common Stock 2021-02-18 4 S 0 845 64.16 D 658943 I See footnote Common Stock 2021-02-18 4 S 0 552 64.17 D 439709 I See footnote Common Stock 2021-02-18 4 S 0 116 65.02 D 658827 I See footnote Common Stock 2021-02-18 4 S 0 75 65.01 D 439634 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 $57.84 to $58.83 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), (14), (15), (16) and (17). 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 $58.86 to $59.82 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $59.86 to $60.70 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $60.90 to $60.97 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $58.24 to $59.22 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $59.24 to $60.23 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $60.25 to $61.24 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $61.25 to $62.23 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $62.25 to $63.19 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $59.63 to $60.52 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $61.17 to $62.01 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $62.52 to $63.46 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $63.65 to $64.62 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $64.68 to $65.15 inclusive. /s/ Keith Regnante, Attorney-in-Fact 2021-02-18