Private Placement, Amendments to Bylaws (Form 8-K)

On December 16, 2025, Larimar Therapeutics, Inc. (the "Company") entered into an exchange agreement (the "Exchange Agreement") with Blue Owl Healthcare Opportunities IV Public Investments LP (the "Stockholder"), pursuant to which the Stockholder exchanged 2,500,000 shares of the Company's common stock, par value $0.001 per share (the "Common Stock"), for 250,000 shares of newly designated Series A convertible preferred stock, a "toothless" preferred stock, par value $0.001 per share (the "Preferred Stock") (the "Exchange").

On December 16, 2025, in connection with the Exchange, the Company filed a Certificate of Designation of Preferences, Rights and Limitations (the "Certificate of Designation") setting forth the preferences, rights and limitations of the Preferred Stock with the Secretary of State of the State of Delaware. Each share of the Preferred Stock will be convertible into 10 shares of Common Stock at the option of the holder at any time, subject to certain limitations, including that the holder will be prohibited from converting Preferred Stock into Common Stock if, as a result of such conversion, the holder, together with its affiliates, would beneficially own a number of shares of Common Stock above a conversion blocker, which is initially set at 9.99% (the "Conversion Blocker") of the total Common Stock then issued and outstanding immediately following the conversion of such shares of Preferred Stock. Holders of the Preferred Stock are permitted to increase the Conversion Blocker to an amount not to exceed 19.99% upon 60 days' notice.

Shares of Preferred Stock will generally have no voting rights, except as required by law and except that the consent of a majority of the holders of the outstanding Preferred Stock will be required to amend the terms of the Preferred Stock. In the event of the Company's liquidation, dissolution or winding up, holders of Preferred Stock will participate pari passu with any distribution of proceeds to holders of Common Stock. Holders of Preferred Stock are entitled to receive when, as and if dividends are declared and paid on the Common Stock, an equivalent dividend, calculated on an as-convertedbasis. Shares of Preferred Stock are otherwise not entitled to dividends.

The Preferred Stock ranks (i) senior to any class or series of capital stock of the Company hereafter created specifically ranking by its terms junior to the Preferred Stock; (ii) on parity with the Common Stock and any class or series of capital stock of the Company created specifically ranking by its terms on parity with the Preferred Stock; and (iii) junior to any class or series of capital stock of the Company created specifically ranking by its terms senior to any Preferred Stock, in each case, as to distributions of assets upon liquidation, dissolution or winding up of the Company, whether voluntarily or involuntarily.

The Exchange closed on December 16, 2025. The Preferred Stock was issued without registration under the Securities Act of 1933, as amended (the "Securities Act"), in reliance on the exemption from registration contained in Section 3(a)(9) of the Securities Act.

The foregoing description of the Exchange Agreement is not complete and is qualified in its entirety by reference to the full text of the Exchange Agreement, which is filed as an exhibit to this Current Report on Form 8-Kand is incorporated by reference herein. A summary of the rights, preferences and privileges of the Preferred Stock described above does not purport to be complete and is qualified in its entirety by reference to the Certificate of Designation, which is filed as an exhibit to this Current Report on Form 8-Kand is incorporated by reference herein.

The information contained above in Item 3.02 of this Current Report on Form 8-Kis hereby incorporated by reference into this Item 5.03.