diff --git a/AGENTS.md b/AGENTS.md
index fdc6278194b4..53a272ea770b 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -7,3 +7,9 @@ algebra operators, without a storage engine of its own.
 ## Security
 
 See [SECURITY.md](./SECURITY.md) before reporting a vulnerability.
+
+## 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.