GT Biopharma, Inc.

Regulatory Filings • Sep 26, 2025

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

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FORM 8-K

CURRENT REPORT

Pursuant to Section 13 OR 15(d) of The Securities Exchange Act of 1934

Date of Report: September 25, 2025

(Date of earliest event reported)

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GT Biopharma, Inc.

(Exact name of registrant as specified in its charter)

Delaware

(State or other Jurisdiction of Incorporation)

1-40023	94-1620407
(Commission
File Number)	(IRS
Employer Identification No.)

N/A 1

(Address of Principal Executive Offices and zip code)

(415) 919-4040

(Registrant’s telephone number, including area code)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of registrant under any of the following provisions:

| ☐ | Written communications
pursuant to Rule 425 under the Securities Act (17 CFR 230.425) |
| --- | --- |
| ☐ | Soliciting material pursuant
to Rule 14a-12(b) under the Exchange Act (17 CFR 240.14a-12(b)) |
| ☐ | Pre-commencement communications
pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) |
| ☐ | Pre-commencement communications
pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c)) |

Securities registered pursuant to Section 12(b) of the Act:

| Title
of each Class | Trading
Symbol(s) | Name
of each Exchange on which registered |
| --- | --- | --- |
| Common stock, $0.001 par
value | GTBP | The Nasdaq Stock Market
LLC |

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☐

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 13(a) of the Exchange Act. ☐

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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.

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Item 3.03 Material Modification to Rights of Security Holders.

As previously disclosed, on each of September 17, 2025, September 18, 2025 and September 23, 2025, certain of the holders of GT Biopharma, Inc.’s Series L 10% Convertible Preferred Stock (the “Series L Preferred Stock”) provided a waiver (the “Waiver”) to the Certificate of Designation of Preferences, Rights and Limitations of Series L 10% Convertible Preferred Stock (the “Certificate of Designations”). On September 25, 2025, an additional holder of Series L Preferred Stock provided a Waiver. Pursuant to the Waiver, all Series L Preferred Stockholders have agreed to waive the rights to redemption set forth in Section 10 of the Certificate of Designations.

The foregoing description of the Waiver does not purport to be complete and is qualified in its entirety by reference to the full text of the Waiver, which is attached hereto as Exhibit 10.1 and is incorporated herein by reference.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits.

Exhibit Number	Description
10.1	Form of Waiver (incorporated by reference to exhibit 10.1 of GT Biopharma, Inc.’s Form 8-K filed with the Securities and Exchange Commission on September 23, 2025)
104	Cover Page Interactive Data File, formatted in Inline
XBRL

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

| /s/ Alan
Urban |
| --- |
| Alan Urban |
| Chief Financial Officer |

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