CRESCENT BIOPHARMA, INC.

As filed with the U.S. Securities and Exchange Commission on January 7, 2026.

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORMS-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Crescent Biopharma, Inc.

(Exact name of registrant as specified in its charter)

300 Fifth Avenue

Waltham, MA 02451

(617) 430-5595

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Joshua Brumm

Chief Executive Officer

Crescent Biopharma, Inc.

300 Fifth Avenue

Waltham, MA 02451

(617) 430-5595

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Approximate date of commencement of proposed sale to the public:

From time to time after the effective date of this Registration Statement.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box. ☒

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the Registration Statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

The information in this preliminary prospectus is not complete and may be changed. The selling securityholders named in this prospectus may not sell the securities until the registration statement filed with the Securities and Exchange Commission is declared effective. This preliminary prospectus is not an offer to sell these securities, and it is not soliciting an offer to buy these securities, in any jurisdiction where the offer or sale is not permitted.

Subject to Completion

Preliminary Prospectus dated January 7, 2026.

PROSPECTUS

19,710,257 Shares

Offered by the Selling Securityholders

This prospectus relates to the proposed resale or other disposition by the selling securityholders identified herein (the “Selling Securityholders”) of up to (i) 13,664,251 (the “Private Placement Shares”) outstanding ordinary shares with a par value of US$0.001 per share (“Ordinary Shares”) issued pursuant to the Private Placement (as defined below), (ii) 131,434 Ordinary Shares (the “Private Placement Pre-Funded Warrant Shares”) issuable upon the exercise of pre-funded warrants (the “Private Placement Pre-Funded Warrants”) issued pursuant to the Private Placement and (iii) 1,387,866 outstanding Ordinary Shares (the “Fairmount Shares”), 1,636,706 Ordinary Shares (the “Fairmount Pre-Funded Warrant Shares”) issuable upon the exercise of pre-funded warrants (the “Fairmount Pre-Funded Warrants”), and 2,890,000 Ordinary Shares (the “Fairmount Series A Conversion Shares”) issuable upon the conversion of Series A non-voting convertible preferred shares (the “Fairmount Series A Shares”), in each case, held by Fairmount Healthcare Fund II L.P. as of immediately prior to the closing of the Private Placement. The Private Placement Shares, the Private Placement Pre-Funded Warrant Shares, the Fairmount Shares, the Fairmount Pre-Funded Warrant Shares and the Fairmount Series A Conversion Shares are referred to herein as the “Resale Shares.”

The Private Placement Shares and Private Placement Pre-Funded Warrants were issued and sold to accredited investors in a private placement, which closed on December 8, 2025 (the “Private Placement”). The Fairmount Shares, Fairmount Pre-Funded Warrants and Fairmount Series A Shares were issued and sold to Fairmount prior to the closing of the Private Placement and were held by Fairmount as of immediately prior the closing of the Private Placement, and Fairmount is a Selling Securityholder hereunder. We are not selling any Resale Shares under this prospectus and will not receive any of the proceeds from the sale or other disposition of Resale Shares by the Selling Securityholders. Upon any exercise of the Private Placement Pre-Funded Warrants or the Fairmount Pre-Funded Warrants by payment of cash, however, we will receive the nominal cash exercise price paid by the holders thereof. We intend to use those proceeds, if any, for general corporate purposes.

The Selling Securityholders may sell the Resale Shares on any national securities exchange or quotation service on which the securities may be listed or quoted at the time of sale, on the over-the-counter market, in one or more transactions otherwise than on these exchanges or systems, such as privately negotiated transactions, or using a combination of these methods, and at fixed prices, at prevailing market prices at the time of the sale, at varying prices determined at the time of sale, or at negotiated prices. See the disclosure under the heading “Plan of Distribution” elsewhere in this prospectus for more information about how the Selling Securityholders may sell or otherwise dispose of their Resale Shares hereunder.

The Selling Securityholders may sell any, all or none of the securities offered by this prospectus and we do not know when or in what amount the Selling Securityholders may sell their Resale Shares hereunder following the effective date of the registration statement of which this prospectus forms a part. Discounts, concessions, commissions and similar selling expenses attributable to the sale of the Resale Shares will be borne by the Selling Securityholders. We will pay certain fees and expenses (other than discounts, concessions, commissions and similar selling expenses) incident to the registration of the Resale Shares with the U.S. Securities and Exchange Commission (“SEC”).

You should carefully read this prospectus and any applicable prospectus supplement before you invest in any of the securities being offered.

Our Ordinary Shares are traded on The Nasdaq Capital Market under the symbol “CBIO.” On January 6, 2026, the last reported sale price for our Ordinary Shares was $11.07 per share.

An investment in our securities involves a high degree of risk. You should carefully consider the information under the heading “Risk Factors” beginning on page 9 of this prospectus and any applicable prospectus supplement.

We are a “smaller reporting company” as defined under the U.S. federal securities laws and, as such, have elected to comply with certain reduced public company reporting requirements.

Neither the Securities and Exchange Commission nor any other regulatory body have approved or disapproved these securities, or passed upon the accuracy or adequacy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is , 2026

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