Material Event (Form 8-K)

Item 8.01. Other Events.

On December 15, 2025, Theriva Biologics, Inc.(the "Company") called to order its Special Meeting of Stockholders (the "Special Meeting"). At that time, there were not present or represented by proxy a sufficient number of shares of the Company's common stock to constitute a quorum. As a result, the Company was not able to convene the Special Meeting. The Company has determined to call a new special meeting to seek approval of the warrant exercsie proposal and adjournment proposal set forth in the proxy statement filed on November 10, 2025. The Company will announce the date and time of the new special meeting and will subsequently file and mail proxy materials as required.

Under that certain warrant inducement agreement (the "Inducement Agreement"), dated October 16, 2025, by and between the Company and certain institutional investors, the Company agreed to use its reasonable best efforts to call a stockholder meeting within 60 days following the closing of the transactions contemplated by the Inducement Agreement for the purpose of seeking approval of the issuance of up to an aggregate of 16,184,560 shares of the Company's common stock upon the exerciseof certain common stock purchase warrants ("New Warrants") issued pursuant to the Inducement Agreement ("Stockholder Approval"). The purpose of the Special Meeting was to seek such Stockholder Approval. Because the Company was not able to convene the Special Meeting, the Company will be required under the Inducement Agreement to call an additional meeting of stockholders every 60 days thereafter to seek Stockholder Approval until the earlier of the date on which Stockholder Approval is obtained or the New Warrants are no longer outstanding.