X0609 4 2026-09-25 0 0001813814 Definium Therapeutics, Inc. DFTX 0001759703 Wiley Matthew T. false C/O DEFINIUM THERAPEUTICS, INC. ONE WORLD TRADE CENTER, SUITE 8500 NEW YORK NY 10007 0 1 0 0 Chief Commercial Officer 1 Common Shares 2026-09-25 4 S 0 3097 36.57 D 359036 D Represents the number of Common Shares sold to satisfy withholding tax obligations in connection with the settlement of vested restricted stock units, pursuant to sell-to-cover elections under a Rule 10b5-1 plan adopted on May 29, 2025. The reported price is a weighted average sales price. These shares were sold in multiple transactions on September 25, 2026 at prices ranging from $36.24 to $36.98. The Reporting Person undertakes to provide 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/ Mark Sullivan, Attorney-in-Fact for Matthew T. Wiley 2026-09-29