diff -r bcc1846e0f2b -r 7834da4b00fa mercurial/revset.py
--- a/mercurial/revset.py	Mon Apr 13 12:17:52 2020 -0400
+++ b/mercurial/revset.py	Mon Apr 13 12:18:29 2020 -0400
@@ -1054,7 +1054,7 @@
 
 @predicate(b'extinct()', safe=True)
 def extinct(repo, subset, x):
-    """Obsolete changesets with obsolete descendants only.
+    """Obsolete changesets with obsolete descendants only. (EXPERIMENTAL)
     """
     # i18n: "extinct" is a keyword
     getargs(x, 0, 0, _(b"extinct takes no arguments"))