X0609 4 2026-08-12 0001649904 RHYTHM PHARMACEUTICALS, INC. RYTM 0001774702 Mazabraud Yann false C/O RHYTHM PHARMACEUTICALS, INC. 222 BERKELEY STREET, 12TH FLOOR BOSTON MA 02116 1 EVP, Head of International 1 Common Stock 2026-08-12 4 M 0 46625 6.80 A 112655 D Common Stock 2026-08-12 4 S 0 2300 111.7992 D 110355 D Common Stock 2026-08-12 4 S 0 1000 112.856 D 109355 D Common Stock 2026-08-12 4 S 0 3605 114.6955 D 105750 D Common Stock 2026-08-12 4 S 0 14568 115.427 D 91182 D Common Stock 2026-08-12 4 S 0 18208 116.4941 D 72974 D Common Stock 2026-08-12 4 S 0 17319 117.4686 D 55655 D Stock Options (Right to Buy) 6.80 2026-08-12 4 M 0 46625 0 D 2032-02-08 Common Stock 46625 35875 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 $111.58 to $112.30 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 $112.84 to $112.92 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 $114.01 to $115.00 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 $115.01 to $116.00 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 $116.01 to $117.00 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. These shares were sold in multiple transactions at prices ranging from $117.01 to $117.60 per share. 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 stock options were granted on February 9, 2022. The options vest and become exercisable in 16 substantially equal installments upon the Reporting Person's completion of each three full months of successive service to the Issuer following the grant date. /s/ Stephen Vander Stoep, attorney-in-fact for Yann Mazabraud 2026-08-14