X0609 4 2026-08-31 0001649904 RHYTHM PHARMACEUTICALS, INC. RYTM 0001636385 Smith Hunter C false C/O RHYTHM PHARMACEUTICALS, INC. 222 BERKELEY STREET, 12TH FLOOR BOSTON MA 02116 1 Chief Financial Officer 1 Common Stock 2026-08-31 4 M 0 57187 25.79 A 176798 D Common Stock 2026-08-31 4 S 0 23072 104.5871 D 153726 D Common Stock 2026-08-31 4 S 0 11514 105.3702 D 142212 D Common Stock 2026-08-31 4 S 0 28188 106.2029 D 114024 D Employee Stock Option (Right to Buy) 25.79 2026-08-31 4 M 0 57187 0 D 2028-02-13 Common Stock 57187 3813 D The exercise and sales reported in this form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on May 13, 2026. The price reported in Column 4 is a weighted average price. The securities were sold in multiple transactions at prices ranging from $104.04 to $105.03 per common stock. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. The price reported in Column 4 is a weighted average price. The securities were sold in multiple transactions at prices ranging from $105.04 to $106.01 per common stock. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. The price reported in Column 4 is a weighted average price. The securities were sold in multiple transactions at prices ranging from $106.05 to $106.88 per common stock. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. This option was granted on February 14, 2018 and the shares underlying this option vested in sixteen equal quarterly installments. /s/ Stephen Vander Stoep, attorney-in-fact for Hunder Smith 2026-09-01