Moleculin Biotech, Inc.

Item 3.03. Material Modifications of Rights of Security Holders. To the extent required by Item 3.03 of Form 8-K, the information contained in Item 5.03 herein is incorporated by reference into this Item 3.03.

Item 5.03 Amendments to Articles of Incorporation or Bylaws; Change in Fiscal Year. At the Moleculin Biotech, Inc. (the “Company”) annual meeting of stockholders completed on October 9, 2026, the stockholders of the Company approved an amendment to the Company’s amended and restated certificate of incorporation (the “Amendment”) to effect the reverse stock split at a ratio in the range of 1-for-2 to 1-for-20, with such ratio to be determined in the discretion of the Company’s board of directors and with such reverse stock split to be effected at such time and date, if at all, as determined by the Company’s board of directors in its sole discretion prior to the one-year anniversary of the annual meeting. Pursuant to such authority granted by the Company’s stockholders, the Company’s board of directors approved a one-for-twenty (1:20) reverse stock split (the “Reverse Stock Split”) of the Company’s common stock and the filing of the Amendment to effectuate the Reverse Stock Split. The Amendment was filed with the Secretary of State of the State of Delaware and the Reverse Stock Split will become effective in accordance with the terms of the Amendment at 12:01 a.m. Eastern Time on October 20, 2026 (the “Effective Time”), and the Company’s common stock will open for trading on The Nasdaq Capital Market on October 20, 2026 on a post-split basis, under the existing ticker symbol “MBRX” but with a new CUSIP number 60855D507. The Amendment provides that, at the Effective Time, every twenty (20) shares of the Company’s issued and outstanding common stock will automatically be combined into one issued and outstanding share of common stock, without any change in par value per share, which will remain $0.001. As a result of the Reverse Stock Split, the number of shares of common stock outstanding will be reduced from approximately 20.91 million shares to approximately 1.05 million shares, and the number of authorized shares of common stock will remain at 500 million shares. In addition, as a result of the Reverse Stock Split, proportionate adjustments will be made to the per share exercise price and/or the number of shares issuable upon the exercise or vesting of all outstanding stock options, restricted stock unit awards and warrants, which will result in a proportional decrease in the number of shares of the Company’s common stock reserved for issuance upon exercise or vesting of such stock options, restricted stock unit awards and warrants, and, in the case of stock options and warrants, a proportional increase in the exercise price of all such stock options and warrants. In addition, the number of shares reserved for issuance under the Company’s equity compensation plan immediately prior to the Effective Time will be reduced proportionately. No fractional shares will be issued as a result of the Reverse Stock Split, and instead, the Company will pay cash (without interest) equal to such fraction multiplied by the average of the closing sales prices of the common stock during the regular trading hours for the five consecutive trading days immediately preceding the Reverse Stock Split. The share amounts set forth in the above paragraph do not take into account any shares which may be paid for in connection with the foregoing treatment of fractional shares. The summary of the Amendment does not purport to be complete and is qualified in its entirety by reference to the full text of the Amendment, a copy of which is attached hereto as Exhibit 3.1 and is incorporated herein by reference.

Item 8.01 Other Events On October 16, 2026, the Company issued a press release to announce that it filed a certificate of amendment to its certificate of incorporation with the Secretary of State of the State of Delaware to effect a 1-for-20 reverse stock split of its common stock. A copy of the press release is attached to this report as Exhibit 99.1 and is incorporated by reference herein. The table below sets forth the impact of the Reverse Stock Split on the Company’s net loss per common share - basic and diluted and weighted average common shares outstanding - basic and diluted, for the years ended December 31, 2025 and 2024, the three months ended March 31, 2026 and 2025, the three and six months ended June 30, 2026 and 2025. Dollars in thousands except share and per share data Pre- Split (1) Post- Split Year ended December 31, Year ended December 31, 2025 2024 2025 2024 Net loss $ (33,560) $ (26,048) $ (33,560) $ (26,048) Net loss available to common stockholders $ (33,664) $ (26,048) $ (33,664) $ (26,048) Net loss per common share - basic and diluted $ (28.42) $ (189.14) $ (568.38) $ (3,782.75) Weighted average common shares outstanding - basic and diluted 1,184,569 137,720 59,228 6,886 Pre- Split (2) Post- Split Three Months Ended March 31, Three Months Ended March 31, 2026 2025 2026 2025 Net loss $ (12,845) $ (5,904) $ (12,845) $ (5,904) Net loss available to common stockholders $ (14,610) $ (5,904) $ (14,610) $ (5,904) Net loss per common share - basic and diluted $ (3.54) $ (15.80) $ (70.85) $ (315.92) Weighted average common shares outstanding - basic and diluted 4,124,482 373,751 206,224 18,688 Pre- Split (2) Post- Split Three Months Ended June 30, Three Months Ended June 30, 2026 2025 2026 2025 Net loss $ (7,635) $ (17,809) $ (7,635) $ (17,809) Net loss available to common stockholders $ (7,964) $ (17,809) $ (7,964) $ (17,809) Net loss per common share - basic and diluted $ (1.40) $ (28.68) $ (28.04) $ (573.50) Weighted average common shares outstanding - basic and diluted 5,680,717 621,056 284,036 31,053 Pre- Split (2) Post- Split Six Months Ended June 30, Six Months Ended June 30, 2026 2025 2026 2025 Net loss $ (20,480) $ (23,713) $ (20,480) $ (23,713) Net loss available to common stockholders $ (22,574) $ (23,713) $ (22,574) $ (23,713) Net loss per common share - basic and diluted $ (4.60) $ (47.61) $ (92.01) $ (952.18) Weighted average common shares outstanding - basic and diluted 4,906,899 498,087 245,345 24,904 (1) The net loss at December 31, 2024 has been retrospectively adjusted for the Company's change in accounting policy during September 30, 2025, from a net loss of $21,763 to $26,048 at December 31, 2024. (2) The pre-split amounts represent amounts from the Company's Quarterly report on Form 10-Q, Note 2 at September 30, 2025.