diff -r a27aa754d6ba -r 41d695a08e90 mercurial/configitems.py
--- a/mercurial/configitems.py	Thu Dec 17 09:35:07 2020 -0800
+++ b/mercurial/configitems.py	Fri Apr 24 16:36:04 2020 +0200
@@ -900,6 +900,11 @@
 )
 coreconfigitem(
     b'experimental',
+    b'evolution.bundle-obsmarker:mandatory',
+    default=True,
+)
+coreconfigitem(
+    b'experimental',
     b'log.topo',
     default=False,
 )