diff --git a/mercurial/repository.py b/mercurial/repository.py
--- a/mercurial/repository.py
+++ b/mercurial/repository.py
@@ -19,6 +19,11 @@
 # we should move this to just "narrow" or similar.
 NARROW_REQUIREMENT = 'narrowhg-experimental'
 
+# When ellipses and shallowing is finalized and the UI is done, there are no
+# more edge cases where things don't work. This should be generalised to shallow
+# or ellipses
+ELLIPSES_REQUIREMENT = 'exp-ellipses'
+
 # Local repository feature string.
 
 # Revlogs are being used for file storage.