X0306 4 2021-03-03 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 2021-03-03 4 S 0 793 55.91 D 643695 I See footnote Common Stock 2021-03-03 4 S 0 518 55.91 D 429765 I See footnote Common Stock 2021-03-03 4 S 0 3004 56.95 D 640691 I See footnote Common Stock 2021-03-03 4 S 0 1958 56.95 D 427807 I See footnote Common Stock 2021-03-03 4 S 0 2903 57.79 D 637788 I See footnote Common Stock 2021-03-03 4 S 0 1894 57.79 D 425913 I See footnote Common Stock 2021-03-03 4 S 0 761 58.88 D 637027 I See footnote Common Stock 2021-03-03 4 S 0 496 58.88 D 425417 I See footnote Common Stock 2021-03-04 4 S 0 1662 54.22 D 635365 I See footnote Common Stock 2021-03-04 4 S 0 1086 54.22 D 424331 I See footnote Common Stock 2021-03-04 4 S 0 2962 55.21 D 632403 I See footnote Common Stock 2021-03-04 4 S 0 1932 55.21 D 422399 I See footnote Common Stock 2021-03-04 4 S 0 1376 56.18 D 631027 I See footnote Common Stock 2021-03-04 4 S 0 895 56.18 D 421504 I See footnote Common Stock 2021-03-04 4 S 0 847 57.21 D 630180 I See footnote Common Stock 2021-03-04 4 S 0 553 57.21 D 420951 I See footnote Common Stock 2021-03-04 4 S 0 193 58.03 D 629987 I See footnote Common Stock 2021-03-04 4 S 0 126 58.03 D 420825 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 $55.39 to $56.32 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) and (12). 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 $56.41 to $57.40 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $57.42 to $58.38 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $58.46 to $59.19 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $53.76 to $54.72 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $54.76 to $55.75 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $55.77 to $56.75 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $56.80 to $57.59 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $57.86 to $58.18 inclusive. /s/ Keith Regnante, Attorney-in-Fact 2021-03-05