Material Agreement (Form 8-K)

Item 1.01 Entry into a Material Definitive Agreement.

Private Placement of Preferred Stock and Warrants

On September 14, 2026, GT Biopharma, Inc. (the "Company") entered into a Securities Purchase Agreement (the "Securities Purchase Agreement") with the purchasers identified therein (collectively, the "Purchasers") providing for the issuance and sale to the Purchasers of (i) up to 8,277.778 shares of the Company's Series M 10% Convertible Preferred Stock (the "Preferred Stock"), (ii) warrants to purchase up to a number of shares of common stock of the Company (the "Common Stock") equal to 100% of the shares of the Company's Common Stock issuable upon conversion of the shares of Preferred Stock (the "Common Warrants"), and (iii) warrants to purchase up to a number of shares of the Company's Common Stock equal to the number of Greenshoe Conversion Shares (as defined in the Securities Purchase Agreement) issuable upon exercise of the Greenshoe Right (as defined below) (the "Vesting Warrants" and together with the Common Warrants, the "Warrants"), with an aggregate stated value of $8,277,778, for an aggregate purchase price of $7,450,000 (the "Offering").

Pursuant to the Securities Purchase Agreement, each Purchaser may elect to purchase shares of Preferred Stock with an aggregate stated value of up to $33,333,333 (the "Greenshoe Rights") for an aggregate purchase price of $30,000,000, subject to adjustments, as further described in the Securities Purchase Agreement. Each Purchaser is entitled to exercise its respective Greenshoe Rights for an amount of Preferred Stock equal to the ratio of such Purchaser's original subscription amount to the original aggregate subscription amount of all Purchasers.

Pursuant to the Certificate of Designation of Preferences, Rights and Limitations of Series M 10% Convertible Preferred Stock (the "Certificate of Designation"), and subject to certain ownership limitations, the Preferred Stock may be converted at any time at the option of the Purchasers into shares of the Company's Common Stock at an initial conversion price of $6.10, subject to certain conditions, as further described in the Certificate of Designation. In addition, the holders of the Preferred Stock are entitled to receive cumulative dividends at the rate per share (as a percentage of the stated value per share) of 10% per annum until September 13, 2027, increasing to 12% per annum thereafter, payable quarterly on January 1, April 1, July 1 and October 1, beginning on the first such date after the date of issuance of the Preferred Stock and on each Conversion Date (as defined in the Certificate of Designation), with respect only to Preferred Stock being converted, in cash, shares of the Company's Common Stock (subject to the Company's satisfaction of the conditions set forth in the Certificate of Designation), or a combination thereof.

Pursuant to the Securities Purchase Agreement, each Purchaser will be issued (i) a Common Warrant, each to purchase up to a number of shares of the Company's Common Stock equal to 100% of the Conversion Shares underlying the Preferred Shares issued to such Purchaser and (ii) a Vesting Warrant (the exercisability of which shall vest ratably from time to time in proportion to the Purchaser's (or its permitted assigns') exercise of such Purchaser's Greenshoe Rights pursuant to Section 2.4 of the Securities Purchase Agreement), each to purchase up to a number of shares of the Company's Common Stock equal to the number of Greenshoe Conversion Shares (as defined in the Securities Purchase Agreement) applicable to such Purchaser, in accordance with the Securities Purchase Agreement. The Common Warrants have an initial exercise price of $6.10 per share, are exercisable, subject to certain ownership limitations, immediately upon issuance and have a term of exercise equal to five years. The Vesting Warrants have an initial exercise price of $6.10 per share, are exercisable, subject to certain vesting and ownership limitations, and have a term of exercise equal to five years from the date that the applicable warrant shares vest.

The Preferred Shares and Warrants both have full ratchet price protection and are subject to other adjustments (including for reverse and forward splits, recapitalizations and similar transactions), as further described in the Certificate of Designation or the Warrants, as applicable. With respect to adjustments in connection with the exercise of Greenshoe Rights, in the first instance, there will not be a floor price; provided, however, if the Company receives written notice from The Nasdaq Stock Market that a floor price should be implemented, a floor price of $1.282 shall be set.

The securities in the Offering were offered privately pursuant to Rule 506(b) of Regulation D under the Securities Act of 1933, as amended.

Registration Rights Agreement

The Company and the Purchasers entered into a registration rights agreement (the "Registration Rights Agreement") pursuant to which the Company agreed to file a registration statement with the Securities and Exchange Commission (the "SEC") covering the public resale of the shares of Common Stock issuable upon conversion of the Preferred Stock and upon exercise of the Warrants. The Company has agreed to file a registration statement within thirty (30) days after the initial closing and after each closing of the exercise of a Greenshoe Right in accordance with the Securities Purchase Agreement, to become effective no later than sixty (60) days after the Closing Date (as defined in the Securities Purchase Agreement) or each Trigger Date (as defined in the Registration Rights Agreement), or in the event of a "full review" by the SEC, ninety (90) days after the Closing Date or each Trigger Date. If these deadlines are not met, the Company will be liable for partial liquidated damages of 1.5% of the subscription amount paid by each Purchaser pursuant to the Securities Purchase Agreement. Further, if the Company fails to pay such liquidated damages within seven days from the date payable, the Company will pay interest thereon at the prime rate plus 12% to each holder of the registerable securities.