X0609 4 2026-07-16 false 0001755237 Cyclerion Therapeutics, Inc. CYCN 0001478485 Hecht Peter M false C/O CYCLERION THERAPEUTICS, INC. 245 FIRST STREET, 18TH FLOOR CAMBRIDGE MA 02142 true false true false false Common Stock 2026-07-16 4 C false 351037 A 910240 D Common Stock 24 I The 2000 Trust for Alexis Mae Hecht Common Stock 24 I The 2000 Trust for Malcolm Paul Hecht Common Stock 24 I The 2000 Trust for Zoe Niovi Hecht Series A Convertible Preferred Stock 2026-07-16 4 C false 351037 D Common Stock 351037 0 D On May 19, 2023, the reporting person purchased directly from the Issuer 351,037 shares of Series A Convertible Preferred Stock (the "Series A Preferred Stock") at a price of $8.68 per share in a private placement transaction pursuant to the Stock Purchase Agreement dated as of March 31, 2023 between the reporting person and the Issuer. The Series A Preferred Stock is convertible to Common Stock on a one-for-one basis at the option of the holder thereof. On July 16, 2026, the reporting person converted all 351,037 shares of Series A Convertible Preferred Stock into 351,037 shares of Common Stock. These shares are held in the referenced trust for the benefit of the reporting person's child. The reporting person's spouse is the trustee of this trust. The reporting person disclaims beneficial ownership of these securities, and the filing of this report is not an admission that the reporting person is the beneficial owner of these securities for purposes of Section 16 or any other purpose. All options to purchase Common Stock previously held by the reporting person were cancelled on July 16, 2026. As a result, the reporting person no longer holds options to purchase Common Stock. /s/ Peter M. Hecht 2026-07-20