Item 1.01 Entry into a Material Definitive Agreement. Securities Purchase Agreement On March 6, 2026, Solid Biosciences Inc., a Delaware corporation (the “ Company”), entered into a securities purchase agreement (the “ Securities Purchase Agreement”) with certain institutional accredited investors (the “ Investors”), pursuant to which the Company agreed to issue and sell to the Investors in a private placement an aggregate of 14,973,257 shares of the Company’s common stock, par value $0.001 per share (the “ Shares”), at a price of $5.61 per share, and, to investors who so choose in lieu of Shares, pre-fundedwarrants to purchase 27,807,482 shares of the Company’s common stock (the “ Pre-Funded”), at a price of $5.609 perPre-FundedWarrant (the “ Private Placement”). The Private Placement is expected to close on or about March 9, 2026, subject to the satisfaction of certain customary closing conditions. The Company expects to receive aggregate gross proceeds from the Private Placement of approximately $240.0 million, before deducting placement agent fees and offering expenses, and aggregate net proceeds from the Private Placement of approximately $226.8 million, after deducting placement agent fees. Leerink Partners LLC and Citigroup Global Markets Inc. acted as joint lead placement agents for the Private Placement. Cantor Fitzgerald & Co. acted as co-leadplacement agent for the Private Placement. H. C. Wainwright & Co. LLC and Truist Securities Inc. acted as co-placementagents for the Private Placement. The Company has granted the Investors indemnification rights with respect to its representations, warranties, covenants and agreements under the Securities Purchase Agreement. The Private Placement includes new and existing investors, including Perceptive Advisors, Bain Capital Life Sciences, RA Capital Management, Invus, Vestal Point Capital, Janus Henderson Investors, and Deep Track Capital, among others. Each Investor has agreed that it will not trade in the Company’s securities until after March 11, 2026. Pre-Funded Each Pre-FundedWarrant to be issued in the Private Placement will have an exercise price of $0.001 per share, will be exercisable immediately and will be exercisable until thePre-FundedWarrant is exercised in full. Under the terms of the Pre-FundedWarrants, the Company may not effect the exercise of any such warrant, and a holder will not be entitled to exercise any portion of any such warrant, if, upon giving effect to such exercise, the aggregate number of shares of common stock beneficially owned by the holder (together with its affiliates, any other persons acting as a group together with the holder or any of the holder’s affiliates, and any other persons whose beneficial ownership of common stock would or could be aggregated with the holder’s for purposes of Section 13(d) or Section 16 of the Securities Exchange Act of 1934, as amended (the “ Exchange Act”)) would exceed 4.99% or 9.99%, as elected by the holder, of the number of shares of common stock outstanding immediately after giving effect to the exercise, as such percentage ownership is determined in accordance with the terms of such warrant, which percentage may be increased or decreased at the holder’s election upon 61 days’ notice to the Company subject to the terms of such warrants, provided that such percentage may in no event exceed 19.99%. Registration Rights Agreement Also on March 6, 2026, the Company entered into a registration rights agreement (the “ Registration Rights Agreement”) with the Investors, pursuant to which the Company agreed to register for resale the Shares and the shares of the Company’s common stock issuable upon exercise of thePre-FundedWarrants (the “Pre-Funded” and, together with the Shares, the “ Registrable Securities”). Under the Registration Rights Agreement, the Company has agreed to file a registration statement covering the resale by the Investors of their Registrable Securities no later than 30 days following the closing of the Private Placement (the “ Filing Date”). The Company has agreed to use reasonable best efforts to cause such registration statement to be declared effective as soon as reasonably practicable and to keep such registration statement effective until the date that all Registrable Securities covered by such registration statement have been sold or can be sold without restriction pursuant to Rule 144

Item 2.02 Results of Operations and Financial Condition. Although the Company has not finalized its full financial results for the fourth quarter and fiscal year ended December 31, 2025, the Company expects to report cash, cash equivalents and available-for-salesecurities of approximately $187.9 million as of December 31, 2025. The estimated cash, cash equivalents and available-for-salesecurities figure is preliminary and unaudited, represents management’s estimate as of the date of this report, is subject to completion of the Company’s financial closing procedures for the fourth quarter and fiscal year ended December 31, 2025, and does not present all necessary information for a complete understanding of the Company’s financial condition as of December 31, 2025, or the Company’s results of operations for the year ended December 31, 2025. The actual financial results may differ materially from the preliminary estimated financial information. The information provided under Item 2.02 of this Current Report on Form8-Kshall not be deemed “filed” for purposes of Section 18 of the Exchange Act or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Item 3.02 Unregistered Sales of Equity Securities. The information contained above in Item 1.01 is hereby incorporated by reference into this Item 3.02. Based in part upon the representations of the Investors in the Securities Purchase Agreement, the offering and sale of the Shares and the Pre-FundedWarrants will be exempt from registration under Section 4(a)(2) of the Securities Act. The Shares and Pre-FundedWarrants have not been registered under the Securities Act or any state securities laws, and the Shares andPre-FundedWarrants may not be offered or sold in the United States absent registration with the SEC or an applicable exemption from the registration requirements. The sale of the securities will not involve a public offering and will be made without general solicitation or general advertising. The Investors represented that they are institutional “accredited investors” as defined in Rule 501(a)(1), (2), (3) or (7) under the Securities Act or “qualified institutional buyers” within the meaning of Rule 144A under the Securities Act, and that they are acquiring the Shares andPre-FundedWarrants for investment purposes only and not with a view to any resale, distribution or other disposition of the Shares andPre-FundedWarrants in violation of the United States federal securities laws.

Item 8.01 Other Events. Based upon the Company’s current operating plan, the Company estimates that the net proceeds from the Private Placement, together with the Company’s existing cash, cash equivalents and available-for-salesecurities, will enable the Company to fund its operating expenses and capital expenditure requirements into the first half of 2028. The Company expects to use the net proceeds from the Private Placement, together with its existing cash, cash equivalents and available-for-salesecurities, to fund ongoing pipeline development programs, business development activities, and the remainder for general and administrative expenses and other general corporate purposes. The Company has based this estimate on assumptions that may prove to be wrong, and the Company could use its available capital resources sooner than it currently expects, in which case it would need to obtain additional funding, which may not be available to the Company on acceptable terms, or at all. The Company does not expect that its existing cash, cash equivalents and available-for-salesecurities and net proceeds from this Private Placement alone will be sufficient to enable the Company to fund the completion of the development of any of its product candidates.

Item 9.01 Financial Statements and Exhibits. (d) Exhibits: Exhibit Description No. ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 4.1 Form of Pre-Funded Warrant. 10.1 Form of Securities Purchase Agreement, dated March 6, 2026, by and among the Company and the other parties thereto. 10.2 Form of Registration Rights Agreement, dated March 6, 2026, by and among the Company and the other parties thereto. 104 Cover Page Interactive Data File (formatted as Inline XBRL). 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. SOLID BIOSCIENCES INC. Date: March 6, 2026 By: /s/ Alexander Cumbo Name: Alexander Cumbo Title: Chief Executive Officer