SCHEDULE 13G/A 0001641172-25-010930 0001219314 XXXXXXXX LIVE 3 Common Stock, no par value 06/30/2025 0001755237 Cyclerion Therapeutics, Inc. 23255M204 245 First Street 18th Floor Cambridge MA 02142 Rule 13d-1(c) Tyndall Capital Partners, L.P. DE 155187.00 0.00 155187.00 0.00 155187.00 N 4.8 PN See Item 2 for additional information. Cyclerion Therapeutics, Inc. 245 First Street, 18th Floor, Cambridge, Massachusetts 02142 The reporting person is Tyndall Capital Partners, L.P. (the "Reporting Person"). As of June 30, 2025, 155,187 shares of common stock, no par value (the "Common Stock"), of Cyclerion Therapeutics, Inc. (the "Issuer") are owned by Tyndall Partners, L.P., a Delaware limited partnership ("Tyndall"). The Reporting Person is the general partner of Tyndall, and possesses the sole power to vote and the sole power to direct the disposition of all shares of Common Stock held by Tyndall. Ownership percentages are based on 3,210,094 shares of Common Stock reported as issued and outstanding as of June 30, 2025 in the Issuer's Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on August 5, 2025. 150 East 58th Street, 14th Floor, New York, New York 10155 Delaware Y 155,187.00 4.8 % 155,187.00 0.00 155,187.00 0.00 N Y Y Y Y Y N By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11. Tyndall Capital Partners, L.P. /s/ Jeffrey S. Halis 08/14/2025