Item 1.01 Entry into a Material Definitive Agreement. Securities Purchase Agreement On January 8, 2024, 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 16,973,103 shares of the Company’s common stock, par value $0.001 per share (the “ Shares”), at a price of $5.53 per share, and, to one Investor in lieu of Shares, pre-fundedwarrants to purchase 2,712,478 shares of the Company’s common stock (the “ Pre-Funded”), at a price of $5.529 perPre-FundedWarrant (the “ Private Placement”). The Private Placement is expected to close on or about January 11, 2024, subject to the satisfaction of certain customary closing conditions. The Company expects to receive aggregate gross proceeds from the Private Placement of approximately $108.9 million, before deducting placement agent fees and offering expenses, and aggregate net proceeds from the Private Placement of approximately $104.1 million, after deducting placement agent fees. Citigroup Global Markets Inc. and Cantor Fitzgerald & Co. acted as joint lead placement agents 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, Adage Capital Partners LP, Deerfield Management Company, Invus, Janus Henderson Investors, Vestal Point Capital, LP, Bain Capital Life Sciences, RA Capital Management and an undisclosed life sciences investor, among others. Pre-Funded Each Pre-Funded Warrantto 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 the Pre-Funded Warrantis exercised in full. Under the terms of the Pre-Funded Warrants, 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% 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 January 8, 2024, 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 commercially reasonable 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 and without the requirement to be in compliance with Rule 144(c)(1) (or any successor thereof) promulgated under the Securities Act of 1933, as amended (the “ Securities Act”). The Company has agreed to be responsible for all fees and expenses incurred in connection with the registration of the Registrable Securities.

Item 2.02. Results of Operations and Financial Condition. Spokespersons of the Company plan to present the information in the presentation attached hereto as Exhibit 99.1 (the “ Presentation”) at various meetings beginning on January 8, 2024, including investor and analyst meetings in connection with the J. P. Morgan Healthcare Conference. A copy of the presentation is attached as Exhibit 99.1 to this Current Report on Form8-Kand is incorporated herein by reference. Although the Company has not finalized its full financial results for the fourth quarter and fiscal year ended December 31, 2023, the Company disclosed in the Presentation that it expects to report cash, cash equivalents and available-for-salesecurities of approximately $123.9 million as of December 31, 2023. 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, 2023, and does not present all necessary information for a complete understanding of the Company’s financial condition as of December 31, 2023, or the Company’s results of operations for the year ended December 31, 2023. 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 Form 8-K (including Exhibit99.1) shall 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 andPre-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 7.01 Regulation FD Disclosure. The information contained above in Item 2.02 related to the Presentation is hereby incorporated by reference into this Item 7.01. The information provided under Item 7.01 of this Current Report on Form8-K(including Exhibit 99.1) shall 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. By providing the information in Item 7.01 of this Current Report on Form8-K(including Exhibit 99.1), the Company is not making an admission as to the materiality of any information herein. The information contained in Item 7.01 of this Current Report on Form8-Kis intended to be considered in the context of more complete information included in the Company’s filings with the SEC and other public announcements that the Company has made and may make from time to time by press release or otherwise. The Company undertakes no duty or obligation to update or revise the information contained in this Current Report on Form8-K, although it may do so from time to time as its management believes is appropriate. Any such updating may be made through the filing of other reports or documents with the SEC, through press releases or through other public disclosures.

Item 8.01 Other Events. On January 8, 2024, the Company issued a press release announcing the Private Placement. The full text of the press release issued in connection with this announcement is attached as Exhibit 99.2 to this Current Report on Form8-Kand incorporated herein by reference. On January 8, 2024, the Company announced that it anticipates providing an initial safety update from cohort 1 of its Phase 1/2 clinical trial, SGT-003-101, a first in human, open-label, multicenter trial to determine the safety and tolerability ofSGT-003in pediatric patients with Duchenne muscular dystrophy, in mid-2024, subject to initiating patient dosing in mid-to-latefirst quarter of 2024, and anticipates providing initial data from cohort 1 of the Phase 1/2 clinical trial in the third quarter of 2024. The Company also announced that it anticipates submitting an investigational new drug application for SGT-501in the first quarter of 2025.

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 January 8, 2024, by and among the Company and the other parties thereto. 10.2 Form of Registration Rights Agreement, dated January 8, 2024, by and among the Company and the other parties thereto. 99.1 Solid Biosciences Inc. Presentation January 2024. 99.2 Press Release, dated January 8, 2024. 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: January 8, 2024 By: /s/ Alexander Cumbo Name: Alexander Cumbo Title: Chief Executive Officer