Common Stock, $0.0001 par value per share

SAB Biotherapeutics, Inc.

777 W 41st St., Suite 401, Miami Beach, FL, 33140

This Schedule 13D/A is being filed on behalf of RA Capital Management, L.P. ("RA Capital"), Peter Kolchinsky, Rajeev Shah, and RA Capital Healthcare Fund, L.P. (the "Fund"). RA Capital, Dr. Kolchinsky, Mr. Shah and the Fund are collectively referred to herein as the "Reporting Persons." The agreement among the Reporting Persons to file this Schedule 13D/A jointly in accordance with Rule 13d-1(k) of the Securities Exchange Act of 1934, as amended, (the "Act") is attached hereto as Exhibit 99.1. The Fund directly holds (i) 4,401,500 shares of common stock; (ii) Series B preferred stock ("Preferred Stock") convertible into up to 12,738,500 shares of common stock at a conversion ratio of 100 shares of common stock per share of Preferred Stock; (iii) Preferred Stock purchase warrants (the "Release Date Warrants") exercisable for up to 85,700 shares of Preferred Stock; and (iv) Preferred Stock purchase warrants (the "Enrollment Date Warrants" and, together with the Release Date Warrants, the "Warrants") exercisable for up to 171,400 shares of Preferred Stock. The Preferred Stock contains a provision (the "Beneficial Ownership Blocker") which precludes conversion of the Preferred Stock to the extent that, following conversion, the Fund, together with its affiliates and other attribution parties, would own more than 9.99% of the common stock outstanding. The Fund is currently prohibited from converting the Preferred Stock by virtue of the Beneficial Ownership Blocker to the extent that such exercise would result in the Reporting Persons' beneficial ownership of more than 5,166,424 shares of common stock. The Fund may decrease or increase the maximum percentage by written notice to the Issuer from time to time to any other percentage not in excess of 19.99%, provided that any increase in the maximum percentage will not be effective until the sixty-first (61st) day after such notice is delivered to the Issuer. RA Capital Healthcare Fund GP, LLC is the general partner of the Fund. 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 the Fund 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 Fund 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 the Fund 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, the Fund 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 13D/A other than for the purpose of determining their obligations under Section 13(d) of the Act, and the filing of this Schedule 13D/A 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.

The address of the principal business office of each of the Reporting Persons is 200 Berkeley Street, 18th Floor, Boston, MA 02116.

The Fund is a private investment vehicle. RA Capital provides investment management services to the Fund. The principal occupation of each of Dr. Kolchinsky and Mr. Shah is investment management.

During the last five years, none of the Reporting Persons has been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree of final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

See Item 6 of the cover pages.

Rows 11 and 13 of each Reporting Person's cover page to this Schedule 13D/A set forth the aggregate number of shares of common stock and percentages of the shares of common stock beneficially owned by such Reporting Person and are incorporated by reference. The percentage set forth in each row 13 is based upon 50,951,037 shares of common stock outstanding as of March 2, 2026, as reported in the Issuer's Annual Report on Form 10-K filed with the SEC on March 9, 2026. Due to field limitations of the EDGAR filing system, the percentage listed in Row 13 of each of the cover pages has been rounded down to 9.9%.

Rows 7 through 10 of each Reporting Person's cover page to this Schedule 13D/A set forth the number of shares of common stock as to which such Reporting Person has the sole or shared power to vote or direct the vote and sole or shared power to dispose or to direct the disposition and are incorporated by reference.

None of the Reporting Persons has effected any transactions with respect to the securities of the Issuer during the past sixty days.

No person (other than the Reporting Persons) is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the securities subject to this Schedule 13D/A.

Not applicable.