diff -r 808f1e38cd1d -r 5645524c6b62 mercurial/revlog.py
--- a/mercurial/revlog.py	Fri Oct 13 16:03:26 2023 +0200
+++ b/mercurial/revlog.py	Fri Oct 13 16:11:04 2023 +0200
@@ -425,7 +425,6 @@
         that test, debug, or performance measurement code might not set this to
         accurate value.
         """
-        self.upperboundcomp = upperboundcomp
 
         self.radix = radix
 
@@ -460,6 +459,7 @@
             self.delta_config = self.opener.options[b'delta-config'].copy()
         else:
             self.delta_config = DeltaConfig()
+        self.delta_config.upper_bound_comp = upperboundcomp
 
         # 3-tuple of (node, rev, text) for a raw revision.
         self._revisioncache = None
@@ -574,6 +574,16 @@
         return self.feature_config.compression_engine
 
     @property
+    def upperboundcomp(self):
+        """temporary compatibility proxy"""
+        util.nouideprecwarn(
+            b"use revlog.delta_config.upper_bound_comp",
+            b"6.6",
+            stacklevel=2,
+        )
+        return self.delta_config.upper_bound_comp
+
+    @property
     def _compengineopts(self):
         """temporary compatibility proxy"""
         util.nouideprecwarn(