Yarrow Bioscience, Inc.

Item 1.01 Entry into a Material Definitive Agreement. On September 10, 2026, Yarrow Bioscience, Inc. (the “Company”) entered into an underwriting agreement (“Underwriting Agreement”) with Jefferies LLC, TD Securities (USA) LLC and Guggenheim Securities, LLC, as the representatives of the underwriters named therein (the “Underwriters”), to issue and sell 5,769,231 shares of the Company’s common stock at a public offering price of $26.00 per share (the “Offering”). In addition, the Company has granted the Underwriters an option (the “Option”) for a period of 30 days to purchase up to an additional 865,384 shares of its common stock at the public offering price, less the underwriting discounts and commissions, which the Underwriters exercised in full on September 11, 2026. The net proceeds from the Offering, including proceeds from the exercise in full of the Option by the Underwriters, are expected to be approximately $161.8 million, after deducting the Underwriters’ discounts and commissions and estimated offering expenses payable by the Company. The securities described above were offered pursuant to the Company’s shelf registration statement on Form S-3 (File No. 333-277609), as amended by Post-Effective Amendment No. 1 thereto, which was declared effective by the U.S. Securities and Exchange Commission (the “SEC”) on August 19, 2026. A final prospectus supplement dated September 10, 2026 relating to and describing the terms of the Offering was filed with the SEC on September 11, 2026. The Offering is expected to close on September 14, 2026. The Underwriting Agreement contains customary representations, warranties and agreements by the Company, customary conditions to closing and other obligations of the parties. In addition, the Company’s directors and executive officers have entered into lock-up agreements pursuant to which they have agreed, subject to certain exceptions, not to sell or otherwise dispose of shares of the Company’s common stock for a period of 60 days after the date of the final prospectus supplement without the prior written consent of Jefferies LLC and TD Securities (USA) LLC. In the Underwriting Agreement, the Company agreed to indemnify the Underwriters against certain liabilities, including liabilities under the Securities Act of 1933, as amended, or to contribute to payments that the Underwriters may be required to make because of such liabilities. A copy of the Underwriting Agreement is filed as Exhibit 1.1 and is incorporated herein by reference. The foregoing description of the Underwriting Agreement does not purport to be complete and is qualified in its entirety by reference to such exhibit. A copy of the opinion of Gibson, Dunn & Crutcher LLP relating to the validity of the issuance and sale of the shares of the common stock in the Offering is filed herewith as Exhibit 5.1.