diff -r 1b5880352314 -r 4bd6e444c76f mercurial/configitems.py
--- a/mercurial/configitems.py	Mon Sep 17 16:52:34 2018 +0800
+++ b/mercurial/configitems.py	Mon Sep 17 17:47:24 2018 +0800
@@ -971,7 +971,7 @@
     default=None,
 )
 coreconfigitem('server', 'bundle2.stream',
-    default=False,
+    default=True,
     alias=[('experimental', 'bundle2.stream')]
 )
 coreconfigitem('server', 'compressionengines',