X0202 SCHEDULE 13G 0001346824 XXXXXXXX LIVE Common Stock, par value $0.0001 per share 05/04/2026 0002114044 Hemab Therapeutics Holdings, Inc. 423494103 101 Main Street, Suite 1220 Cambridge MA 02142 Rule 13d-1(c) RA Capital Management, L.P. DE 0.00 7729773.00 0.00 7729773.00 7729773.00 16.6 IA PN Peter Kolchinsky X1 0.00 7729773.00 0.00 7729773.00 7729773.00 16.6 HC IN Rajeev Shah X1 0.00 7729773.00 0.00 7729773.00 7729773.00 16.6 HC IN RA Capital Healthcare Fund, L.P. DE 0.00 6365783.00 0.00 6365783.00 6365783.00 13.6 PN Hemab Therapeutics Holdings, Inc. 101 Main Street, Suite 1220, Cambridge, MA, 02142. The names of the persons filing this report (collectively, the "Reporting Persons") are: RA Capital Management, L.P. ("RA Capital") Peter Kolchinsky ("Dr. Kolchinsky") Rajeev Shah ("Mr. Shah") RA Capital Healthcare Fund, L.P. (the "Fund") The Reporting Persons expressly disclaim status as a "group" for purposes of this Schedule 13G. The address of the principal business office of each of the Reporting Persons is: c/o RA Capital Management, L.P., 200 Berkeley Street, 18th Floor, Boston MA 02116 RA Capital and the Fund are Delaware limited partnerships. Dr. Kolchinsky and Mr. Shah are United States citizens. Y Row 9 of each Reporting Person's cover page to this Schedule 13G sets forth the aggregate number of shares of common stock of the Issuer beneficially owned by such Reporting Person and is incorporated by reference. The Reporting Persons' ownership of the Issuer's securities includes (i) 6,365,783 shares of common stock held directly by the Fund; (ii)1,009,052 shares of common stock held directly by the RA Capital Nexus II Fund, L.P. (the "Nexus Fund II"); and (iii) 354,938 shares of common stock held directly by the RA Capital Nexus IV Fund, L.P. (the "Nexus Fund IV"). RA Capital Healthcare Fund GP, LLC is the general partner of the Fund, RA Capital Nexus Fund II GP, LLC is the general partner of the Nexus Fund II and RA Capital Nexus Fund IV GP, LLC is the general partner of the Nexus Fund IV. The general partner of RA Capital is RA Capital Management GP, LLC, of which Dr. Kolchinsky and Mr. Shah are the controlling persons. RA Capital serves as investment adviser for each of the Fund, The Nexus Fund II and the Nexus Fund IV and may be deemed a beneficial owner, for purposes of Section 13(d) of the Act, of any securities of the Issuer held by the Fund, the Nexus Fund II or the Nexus Fund IV. Each of the Fund, the Nexus Fund II and the Nexus Fund IV has delegated to RA Capital the sole power to vote and the sole power to dispose of all securities held in its portfolio, including the shares of the Issuer's common stock reported herein. Because each of the Fund, the Nexus Fund II and the Nexus Fund IV has divested itself of voting and investment power over the reported securities it holds and may not revoke that delegation on less than 61 days' notice, each of the Fund, the Nexus Fund II and the Nexus Fund IV disclaims beneficial ownership of the securities it holds for purposes of Section 13(d) of the Act and therefore disclaims any obligation to report ownership of the reported securities under Section 13(d) of the Act. As managers of RA Capital, Dr. Kolchinsky and Mr. Shah may be deemed beneficial owners, for purposes of Section 13(d) of the Act, of any securities of the Issuer beneficially owned by RA Capital. RA Capital, Dr. Kolchinsky, and Mr. Shah disclaim beneficial ownership of the securities reported in this Schedule 13G other than for the purpose of determining their obligations under Section 13(d) of the Act, and the filing of this Schedule 13G shall not be deemed an admission that either RA Capital, Dr. Kolchinsky, or Mr. Shah is the beneficial owner of such securities for any other purpose. Row 11 of each Reporting Person's cover page to this Schedule 13G sets forth the percentages of shares of common stock of the Issuer beneficially owned by such Reporting Person and is incorporated by reference. The percentage set forth in each row 11 is based upon 46,705,410 shares outstanding as of May 4, 2026, as reported in the Issuer's final prospectus dated April 30, 2026 filed with the Securities and Exchange Commission (the "SEC") on May 1, 2025. Row 5 of each Reporting Person's cover page to this Schedule 13G sets forth the sole power to vote or to direct the vote of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference. Row 6 of each Reporting Person's cover page to this Schedule 13G sets forth the shared power to vote or to direct the vote of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference. Row 7 of each Reporting Person's cover page to this Schedule 13G sets forth the sole power to dispose or to direct the disposition of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference. Row 8 of each Reporting Person's cover page to this Schedule 13G sets forth the shared power to dispose or to direct the disposition of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference. Y Y Y Y Y N By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11. Exhibit 99.1 Joint Filing Agreement RA Capital Management, L.P. /s/ Peter Kolchinsky 05/11/2026 Peter Kolchinsky /s/ Peter Kolchinsky 05/11/2026 Rajeev Shah /s/ Rajeev Shah 05/11/2026 RA Capital Healthcare Fund, L.P. /s/ Peter Kolchinsky 05/11/2026