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Exhibit 31.1

CERTIFICATION OF PRINCIPAL EXECUTIVE OFFICER

PURSUANT TO SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002

I, Joshua Brumm, certify that:

1.I have reviewed this Amendment No. 1 to the Quarterly Report on Form 10-Q/A of Crescent Biopharma, Inc.; and

2.Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report.

Date: June 22, 2026
/s/ Joshua Brumm
Joshua Brumm
Chief Executive Officer
(Principal Executive Officer)