GT Biopharma, Inc.

S-11 forms-1.htm S-1

As filed with the Securities and Exchange Commission on October 9, 2026.

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

GT BIOPHARMA, INC.

(Exact Name of Registrant as Specified in Its Charter)

N/A 1

(415) 919-4040

(Address, Including Zip Code, and Telephone Number, Including Area Code, of Registrant’s Principal Executive Offices)

Michael Breen

Chief Executive Officer

N/A 1

(415) 919-4040

(Name, Address, Including Zip Code, and Telephone Number, Including Area Code, of Agent For Service)

Copies to:

Alan A. Lanis, Jr.

Baker & Hostetler LLP

1900 Avenue of the Stars, Suite 2700

Los Angeles, CA 90067

Tel: (310) 820-8800

Approximate date of commencement of proposed sale to the public: As soon as practicable 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, please 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 files 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, as amended, or until the registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

1 Effective as of July 1, 2024, the Company became a fully remote company. We do not maintain a principal executive office. For purposes of compliance with applicable requirements of the Securities Act of 1933, as amended, and the Securities Exchange Act of 1934, as amended, any stockholder communication required to be sent to the Company’s principal executive offices may be directed to 505 Montgomery Street, 10th Floor, San Francisco, California 94111, or by email to auditcommittee@gtbiopharma.com.

The information in this preliminary prospectus is not complete and may be changed. These securities may not be sold until the registration statement filed with the Securities and Exchange Commission is 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 state where the offer or sale is not permitted.

SUBJECT TO COMPLETION DATED OCTOBER 9, 2026

PRELIMINARY PROSPECTUS

13,502,835 Shares of Common Stock

This prospectus relates to the offering from time to time by the selling stockholders named in this prospectus (the “Selling Stockholders”) of up to an aggregate 13,502,835 shares of common stock, par value $0.001 per share (the “Common Stock”), of GT Biopharma, Inc., a Delaware corporation (the “Company”), consisting of (i) 6,716,931 shares of Common Stock issuable upon the conversion of 8,611.111 shares of Series M 10% Convertible Preferred Stock, par value $0.01 per share (the “Series M Preferred Stock” or the “Series M Preferred Shares,” and the shares of Common Stock issuable upon conversion of the Series M Preferred Shares, the “Series M Conversion Shares”) issued in connection with our private placement in September 2026, (ii) 6,716,931 shares of Common Stock issuable upon the exercise of warrants (the “Series M Common Stock Warrants” and the shares of Common Stock issuable upon exercise of the Series M Common Stock Warrants, the “Series M Common Stock Warrant Shares”) issued in connection with our private placement in September 2026, (iii) 30,004 shares of Common Stock issuable upon the conversion of 340.556 shares of Series L 10% Convertible Preferred Stock (the “Series L Preferred Stock” or the “Series L Preferred Shares,” and the shares of Common Stock issuable upon conversion of the Series L Preferred Shares, the “Series L Conversion Shares”) issued in connection with our private placement in May 2025, and together with the Series M Conversion Shares, the “Conversion Shares”, (iv) 30,004 shares of Common Stock issuable upon the exercise of warrants issuable upon exercise of the Series L Greenshoe Rights (as defined below) (the “Series L Vesting Warrants” and the shares of Common Stock issuable upon exercise of the Series L Vesting Warrants, the “Series L Vesting Warrant Shares”) issued in connection with our private placement in May 2025, and together with the Series M Common Stock Warrants, the “Warrants,” (v) 6,996 shares of Common Stock issued to the holders of Series L Preferred Stock of record as of June 24, 2026 as a dividend, which represents a rate per share of 11.1% per annum of the outstanding stated value of the Series L Preferred Stock, payable on July 1, 2026 (the “Q2 Dividend Shares”); and (vi) 1,969 shares of Common Stock issued to the holders of Series L Preferred Stock of record as of September 29, 2026 as a dividend, which represents a rate per share of 12% per annum of the outstanding stated value of the Series L Preferred Stock, payable on October 1, 2026 (the “Q3 Dividend Shares” and together with the Q2 Dividend Shares, the “Dividend Shares”). The Conversion Shares, the Series M Common Stock Warrant Shares, the Series L Vesting Warrant Shares and the Dividend Shares are collectively referred to as the “Shares.” We are registering the Shares on behalf of the Selling Stockholders, to be offered and sold by them from time to time. We will not receive any proceeds from the sale of the Shares offered by this prospectus.

We have agreed to bear all of the expenses incurred in connection with the registration of the Shares. The Selling Stockholders will pay or assume discounts, commissions, fees of underwriters, selling brokers or dealer managers and similar expenses, if any, incurred for the sale of the Shares of our Common Stock.

The Selling Stockholders, or their respective donees, pledgees, transferees or other successors-in-interest, may sell or otherwise dispose of the Shares covered by this prospectus in a number of different ways. We provide more information about how the Selling Stockholders may sell or otherwise dispose of their Shares in the section entitled “Plan of Distribution.” For a list of the Selling Stockholders, see the section entitled “Selling Stockholders.”

Our Common Stock is presently listed on the Nasdaq Capital Market (“Nasdaq”) under the trading symbol “GTBP.” On October 8, 2026, the closing sale price for our Common Stock was $5.96 per share.

Investing in our securities involves a high degree of risk. See the section entitled “Risk Factors” beginning on page 8 of this prospectus and in the documents incorporated by reference into this prospectus for a discussion of risks that should be considered in connection with an investment in our securities.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is , 2026.

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