diff --git a/modules/environments/hermes-agent/default.nix b/modules/environments/hermes-agent/default.nix
index 0547df8..4ef01d6 100644
--- a/modules/environments/hermes-agent/default.nix
+++ b/modules/environments/hermes-agent/default.nix
@@ -19,7 +19,7 @@ in
     services.hermes-agent = {
       enable = true;
       # Deliberate pin, matches the approved design — bump on purpose, not by drift.
-      settings.model.default = "anthropic/claude-sonnet-4-5";
+      settings.model.default = "anthropic/claude-sonnet-5-5";
       # The Nix flake input is the source of truth for hermes's version here; its
       # built-in self-updater polling GitHub independently just burns API quota.
       settings.updates.check = false;