Amendment to Annual Report (Form 10-K/A)

Cyclerion Therapeutics, Inc. (the "Company") is filing this Amendment No. 1 (the "Amendment") to its Annual Report on Form 10-K for the fiscal year ended December 31, 2024, which was originally filed with the Securities and Exchange Commission (the "Commission") on March 4, 2025 (the "Original 10-K"), for the purpose of amending Item 8 of the Original 10-K to amend the Report of Independent Registered Public Accounting Firm of Ernst & Young LLP on the Company's financial statements as of and for the years ended December 31, 2024 and 2023 (the "Original Audit Report"). The only change to the Original Audit Report is to add an additional paragraph regarding "Critical Audit Matter" which paragraph was inadvertently omitted by Ernst & Young LLP from the Original Audit Report. The information contained in this additional paragraph relates to information presented in Notes 2 and 5 to the Notes to Financial Statements contained in the Original 10-K.The Original Audit Report, as amended (the "Amended Audit Report") appears on page F-2 of this Amendment along with the Financial Statements and Notes to the Financial Statements, which remain otherwise unchanged from those contained in the Original 10-K filing.

In accordance with Rule 12b-15 under the Securities Exchange Act of 1934, this Amendment also includes currently dated certifications from the Company's principal executive officer and principal financial officer as required by Sections 302 and 906 of the Sarbanes-Oxley Act of 2002. As required by the rules of the Commission, this Amendment sets forth an amended "Item 15. Exhibits, Financial Statement Schedules" in its entirety, which includes the currently dated certifications of the Company's principal executive officer and principal financial officer as Exhibits 31.1, 31.2, 32.1 and 32.2 as well as Exhibit 23.1, the Independent Registered Public Accounting Firm's Consent. This Amendment does not otherwise update any exhibits contained in the Original 10-K.

Except as described above, no other changes have been made to the Original 10-K. The Original 10-K continues to be as of the dates described in the Original 10-K, and the Company has not updated the disclosures contained therein to reflect any events that occurred subsequent to such dates. Accordingly, this Amendment should be read in conjunction with the Company's filings made with the Commission subsequent to the filing of the Original 10-K, as information in such filings may update or supersede certain information contained in this Amendment.

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