diff -r 133f5a54ed9d -r 774c00348f9f mercurial/localrepo.py
--- a/mercurial/localrepo.py	Tue Oct 10 10:02:21 2023 +0200
+++ b/mercurial/localrepo.py	Tue Oct 10 10:02:29 2023 +0200
@@ -1087,7 +1087,7 @@
     # experimental config: format.chunkcachesize
     chunkcachesize = ui.configint(b'format', b'chunkcachesize')
     if chunkcachesize is not None:
-        options[b'chunkcachesize'] = chunkcachesize
+        data_config.chunk_cache_size = chunkcachesize
 
     deltabothparents = ui.configbool(
         b'storage', b'revlog.optimize-delta-parent-choice'