diff --git a/AGENTS.md b/AGENTS.md
index 565e4252f80..157ba35f7c4 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -15,3 +15,9 @@ code targets JDK 17. To test under a specific JDK pass build parameters:
 - `-PjdkTestVendor=<vendor>` / `-PjdkTestImplementation=<impl>` — pin the vendor / VM implementation (jdkTestVersion is enough for most cases)
 
 List every available build parameter with `./gradlew parameters`.
+
+## Commit messages
+
+Always end commit messages, including drafts, with `Assisted-by: <tool> (<model-id>)`,
+never `Co-Authored-By:`. Keep existing trailers and add yours when amending someone
+else's commit.