diff -r 9989a276712f -r 7015b0232c5e mercurial/bundle2.py
--- a/mercurial/bundle2.py	Fri Jan 29 16:33:12 2021 -0800
+++ b/mercurial/bundle2.py	Thu Mar 04 21:58:55 2021 +0100
@@ -1598,7 +1598,6 @@
     b'digests': tuple(sorted(util.DIGESTS.keys())),
     b'remote-changegroup': (b'http', b'https'),
     b'hgtagsfnodes': (),
-    b'rev-branch-cache': (),
     b'phases': (b'heads',),
     b'stream': (b'v2',),
 }
@@ -1643,6 +1642,9 @@
     # Else always advertise support on client, because payload support
     # should always be advertised.
 
+    # b'rev-branch-cache is no longer advertised, but still supported
+    # for legacy clients.
+
     return caps