diff --git a/changelog.d/17105.misc b/changelog.d/17105.misc
new file mode 100644
index 000000000..d4443b89c
--- /dev/null
+++ b/changelog.d/17105.misc
@@ -0,0 +1 @@
+Enabled MSC3266 by default in the synapse complement image.
diff --git a/docker/complement/conf/workers-shared-extra.yaml.j2 b/docker/complement/conf/workers-shared-extra.yaml.j2
index a2c378f54..4c41ee770 100644
--- a/docker/complement/conf/workers-shared-extra.yaml.j2
+++ b/docker/complement/conf/workers-shared-extra.yaml.j2
@@ -102,6 +102,8 @@ experimental_features:
   msc3874_enabled: true
   # no UIA for x-signing upload for the first time
   msc3967_enabled: true
+  # Expose a room summary for public rooms
+  msc3266_enabled: true
 
   msc4115_membership_on_events: true