Merge 8ea6744ae0 into f92c3579ac

changelogs/room_versions/newsfragments/2303.clarification

@@ -1 +0,0 @@
-Remove the post-1.16 release note for room version 12.

content/rooms/_index.md

@@ -56,6 +56,19 @@ Clients should not ask room administrators to upgrade their rooms if the
 room is running a stable version. Servers SHOULD use **room version 12** as
 the default room version when creating new rooms.
 
+{{% boxes/note %}}
+
+{{% added-in v="1.16" %}}
+
+Room version 12 is introduced and made default in this specification release.
+Servers are encouraged to continue using room version 11 as the default room
+version for the early days and weeks following this specification release,
+and then gradually switch the default over when they deem appropriate.
+
+<!-- TODO(SCT): Remove this note box in Matrix 1.17 -->
+
+{{% /boxes/note %}}
+
 The available room versions are:
 
 -   [Version 1](/rooms/v1) - **Stable**. The initial room version.