X0508 4 2023-11-20 0001759138 Cabaletta Bio, Inc. CABA 0001791742 Binder Gwendolyn C/O CABALETTA BIO, INC. 2929 ARCH STREET, SUITE 600 PHILADELPHIA PA 19104 false true false false See Remarks false Common Stock 2023-11-20 4 M false 11000 1.01 A 31000 D Common Stock 2023-11-20 4 S false 3542 17.3937 D 27458 D Common Stock 2023-11-20 4 S false 7458 18.0216 D 20000 D Stock Option (Right to Buy) 1.01 2023-11-20 4 M false 11000 0.00 D 2028-10-28 Common Stock 11000 122756 D These transactions were effected pursuant to a Rule 10b5-1 trading plan dated January 20, 2023 adopted by the Reporting Person. The price reported in column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $16.90 - $17.89. 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 $17.90 - $18.24. 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 vests over four years, with 25% vested on October 11, 2019, and the remaining shares vesting in 12 equal quarterly installments thereafter. President, Science & Technology By: /s/ Michael Gerard, as Attorney-in-Fact 2023-11-21