diff --git a/changelog.d/10161.removal b/changelog.d/10161.removal
new file mode 100644
index 000000000000..d4411464c7f6
--- /dev/null
+++ b/changelog.d/10161.removal
@@ -0,0 +1 @@
+Stop supporting the unstable spaces prefixes from MSC1772.
diff --git a/synapse/api/constants.py b/synapse/api/constants.py
index 8d5b2177d2ab..f6fa7b1eac05 100644
--- a/synapse/api/constants.py
+++ b/synapse/api/constants.py
@@ -112,8 +112,6 @@ class EventTypes:
 
     SpaceChild = "m.space.child"
     SpaceParent = "m.space.parent"
-    MSC1772_SPACE_CHILD = "org.matrix.msc1772.space.child"
-    MSC1772_SPACE_PARENT = "org.matrix.msc1772.space.parent"
 
 
 class ToDeviceEventTypes:
@@ -180,7 +178,6 @@ class EventContentFields:
 
     # cf https://github.com/matrix-org/matrix-doc/pull/1772
     ROOM_TYPE = "type"
-    MSC1772_ROOM_TYPE = "org.matrix.msc1772.type"
 
 
 class RoomEncryptionAlgorithms:
diff --git a/synapse/handlers/space_summary.py b/synapse/handlers/space_summary.py
index 046dba6fd87a..73d2aab15c20 100644
--- a/synapse/handlers/space_summary.py
+++ b/synapse/handlers/space_summary.py
@@ -402,10 +402,7 @@ async def _summarize_remote_room(
             return (), ()
 
         return res.rooms, tuple(
-            ev.data
-            for ev in res.events
-            if ev.event_type == EventTypes.MSC1772_SPACE_CHILD
-            or ev.event_type == EventTypes.SpaceChild
+            ev.data for ev in res.events if ev.event_type == EventTypes.SpaceChild
         )
 
     async def _is_room_accessible(
@@ -514,11 +511,6 @@ async def _build_room_entry(self, room_id: str) -> JsonDict:
             current_state_ids[(EventTypes.Create, "")]
         )
 
-        # TODO: update once MSC1772 lands
-        room_type = create_event.content.get(EventContentFields.ROOM_TYPE)
-        if not room_type:
-            room_type = create_event.content.get(EventContentFields.MSC1772_ROOM_TYPE)
-
         room_version = await self._store.get_room_version(room_id)
         allowed_spaces = None
         if await self._event_auth_handler.has_restricted_join_rules(
@@ -540,7 +532,7 @@ async def _build_room_entry(self, room_id: str) -> JsonDict:
             ),
             "guest_can_join": stats["guest_access"] == "can_join",
             "creation_ts": create_event.origin_server_ts,
-            "room_type": room_type,
+            "room_type": create_event.content.get(EventContentFields.ROOM_TYPE),
             "allowed_spaces": allowed_spaces,
         }
 
@@ -569,9 +561,7 @@ async def _get_child_events(self, room_id: str) -> Iterable[EventBase]:
             [
                 event_id
                 for key, event_id in current_state_ids.items()
-                # TODO: update once MSC1772 has been FCP for a period of time.
-                if key[0] == EventTypes.MSC1772_SPACE_CHILD
-                or key[0] == EventTypes.SpaceChild
+                if key[0] == EventTypes.SpaceChild
             ]
         )