diff --git a/README.md b/README.md
index a0af77fc..25155152 100644
--- a/README.md
+++ b/README.md
@@ -92,6 +92,9 @@ work:
 experimental_features:
     # MSC3266: Room summary API. Used for knocking over federation
     msc3266_enabled: true
+    # MSC4222 needed for syncv2 state_after. This allow clients to
+    # correctly track the state of the room.
+    msc4222_enabled: true
 
 # The maximum allowed duration by which sent events can be delayed, as
 # per MSC4140.
@@ -109,6 +112,10 @@ summary contains the room join rules. We need that to decide if the user gets
 prompted with the option to knock ("Request to join call"), a cannot join error or the
 join view.
 
+MSC4222 allow clients to opt-in to a change of the sync v2 API that allows them
+to correctly track the state of the room. This is required by Element Call to
+track room state reliably.
+
 Element Call requires a Livekit SFU alongside a [Livekit JWT
 service](https://github.com/element-hq/lk-jwt-service) to work. The url to the
 Livekit JWT service can either be configured in the config of Element Call
diff --git a/backend/dev_homeserver.yaml b/backend/dev_homeserver.yaml
index b41de45b..5697c32e 100644
--- a/backend/dev_homeserver.yaml
+++ b/backend/dev_homeserver.yaml
@@ -25,6 +25,9 @@ trusted_key_servers:
 experimental_features:
   # MSC3266: Room summary API. Used for knocking over federation
   msc3266_enabled: true
+  # MSC4222 needed for syncv2 state_after. This allow clients to
+  # correctly track the state of the room.
+  msc4222_enabled: true
 
 # The maximum allowed duration by which sent events can be delayed, as
 # per MSC4140. Must be a positive value if set.  Defaults to no