--- a/mercurial/branchmap.py	Mon Jun 24 03:16:52 2024 +0200
+++ b/mercurial/branchmap.py	Mon Jun 24 10:52:46 2024 +0200
@@ -867,7 +867,7 @@
     ignored.
     """
 
-    _base_filename = b"branch3"
+    _base_filename = b"branch3-exp"
     _default_key_hashes = (None, None)
 
     def __init__(self, *args, pure_topo_branch=None, **kwargs):