X0609 4 2026-08-13 0001649904 RHYTHM PHARMACEUTICALS, INC. RYTM 0002027261 Garfield Alastair false C/O RHYTHM PHARMACEUTICALS, INC. 222 BERKELEY STREET, 12TH FLOOR BOSTON MA 02116 1 Chief Scientific Officer 1 Common Stock 2026-08-13 4 S 0 2007 116.1093 D 8051 D Common Stock 2026-08-13 4 S 0 1556 117.0759 D 6495 D Common Stock 2026-08-13 4 S 0 3400 118.2843 D 3095 D Common Stock 2026-08-13 4 S 0 800 119.1688 D 2295 D The sales reported in the Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on May 14, 2026. The price reported in Column 4 is a weighted average price. The securities were sold in multiple transactions at prices ranging from $115.67 to $116.62 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 $116.72 to $117.66 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 $117.73 to $118.71 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 $118.73 to $119.52 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. /s/ Stephen Vander Stoep, attorney-in-fact for Alastair Garfield 2026-08-17