diff --git a/Annex/Branch.hs b/Annex/Branch.hs
index 8f927a78b4..42942d886f 100644
--- a/Annex/Branch.hs
+++ b/Annex/Branch.hs
@@ -500,11 +500,19 @@ append jl f appendable toappend = do
 {- Commit message used when making a commit of whatever data has changed
  - to the git-annex branch. -}
 commitMessage :: Annex String
-commitMessage = fromMaybe "update" . annexCommitMessage <$> Annex.getGitConfig
+commitMessage = fromMaybe "update" <$> getCommitMessage
 
 {- Commit message used when creating the branch. -}
 createMessage :: Annex String
-createMessage = fromMaybe "branch created" . annexCommitMessage <$> Annex.getGitConfig
+createMessage = fromMaybe "branch created" <$> getCommitMessage
+
+getCommitMessage :: Annex (Maybe String)
+getCommitMessage = do
+	config <- Annex.getGitConfig
+	case annexCommitMessageCommand config of
+		Nothing -> return (annexCommitMessage config)
+		Just cmd -> catchDefaultIO (annexCommitMessage config) $
+			Just <$> liftIO (readProcess "sh" ["-c", cmd])
 
 {- Stages the journal, and commits staged changes to the branch. -}
 commit :: String -> Annex ()
diff --git a/CHANGELOG b/CHANGELOG
index 8057fb3c81..e4d178c408 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -11,6 +11,7 @@ git-annex (10.20240130) UNRELEASED; urgency=medium
   * stack.yaml: Update to lts-22.9 and use crypton.
   * assistant, undo: When committing, let the usual git commit
     hooks run.
+  * Added annex.commitmessage-command config.
 
  -- Joey Hess <id@joeyh.name>  Mon, 29 Jan 2024 15:59:33 -0400
 
diff --git a/Types/GitConfig.hs b/Types/GitConfig.hs
index f9e0149ddb..f97ee52192 100644
--- a/Types/GitConfig.hs
+++ b/Types/GitConfig.hs
@@ -88,6 +88,7 @@ data GitConfig = GitConfig
 	, annexAlwaysCommit :: Bool
 	, annexAlwaysCompact :: Bool
 	, annexCommitMessage :: Maybe String
+	, annexCommitMessageCommand :: Maybe String
 	, annexMergeAnnexBranches :: Bool
 	, annexDelayAdd :: Maybe Int
 	, annexHttpHeaders :: [String]
@@ -176,6 +177,7 @@ extractGitConfig configsource r = GitConfig
 	, annexAlwaysCommit = getbool (annexConfig "alwayscommit") True
 	, annexAlwaysCompact = getbool (annexConfig "alwayscompact") True
 	, annexCommitMessage = getmaybe (annexConfig "commitmessage")
+	, annexCommitMessageCommand = getmaybe (annexConfig "commitmessage-command")
 	, annexMergeAnnexBranches = getbool (annexConfig "merge-annex-branches") True
 	, annexDelayAdd = getmayberead (annexConfig "delayadd")
 	, annexHttpHeaders = getlist (annexConfig "http-headers")
diff --git a/doc/git-annex.mdwn b/doc/git-annex.mdwn
index c4bd2b8df3..9d61e675a1 100644
--- a/doc/git-annex.mdwn
+++ b/doc/git-annex.mdwn
@@ -1088,6 +1088,11 @@ repository, using [[git-annex-config]]. See its man page for a list.)
   This works well in combination with annex.alwayscommit=false,
   to gather up a set of changes and commit them with a message you specify.
 
+* `annex.commitmessage-command`
+
+  This command is run and its output is used as the commit message to the
+  git-annex branch.
+
 * `annex.alwayscompact`
 
   By default, git-annex compacts data it records in the git-annex branch.
diff --git a/doc/todo/make_annex___34__respect__34___.git__47__hooks__47__prepare-commit-msg/comment_6_b8bb9e5c7156e4defd7a2e8b7777e1ba._comment b/doc/todo/make_annex___34__respect__34___.git__47__hooks__47__prepare-commit-msg/comment_6_b8bb9e5c7156e4defd7a2e8b7777e1ba._comment
new file mode 100644
index 0000000000..4aa985a935
--- /dev/null
+++ b/doc/todo/make_annex___34__respect__34___.git__47__hooks__47__prepare-commit-msg/comment_6_b8bb9e5c7156e4defd7a2e8b7777e1ba._comment
@@ -0,0 +1,18 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 6"""
+ date="2024-02-12T17:36:32Z"
+ content="""
+Turns out that the assistant doesn't commit to the git-annex branch itself,
+instead the pre-commit hook runs `git-annex pre-commit`, and 
+the git-annex branch commit on process shutdown is where the commit
+happens.
+
+A bit surprising! If the pre-commit hook didn't run git-annex, 
+the assistant would later explicitly commit the branch before
+pushing to remotes.
+
+Anyway, this does mean you can rely on the git-annex branch commit
+happening after the working tree commit. At least, when there are
+no other git-annex processes running.
+"""]]