diff --git a/changelogs/client_server/newsfragments/2158.feature b/changelogs/client_server/newsfragments/2158.feature
new file mode 100644
index 00000000..f9275b0d
--- /dev/null
+++ b/changelogs/client_server/newsfragments/2158.feature
@@ -0,0 +1 @@
+Add `/_matrix/client/v1/room_summary/{roomIdOrAlias}` and extend `/_matrix/client/v1/rooms/{roomId}/hierarchy` with the new optional properties `allowed_room_ids`, `encryption` and `room_version` as per [MSC3266](https://github.com/matrix-org/matrix-spec-proposals/pull/3266).
diff --git a/data/api/client-server/definitions/public_rooms_chunk.yaml b/data/api/client-server/definitions/public_rooms_chunk.yaml
index 89e76059..33276662 100644
--- a/data/api/client-server/definitions/public_rooms_chunk.yaml
+++ b/data/api/client-server/definitions/public_rooms_chunk.yaml
@@ -17,6 +17,8 @@ title: "PublishedRoomsChunk"
 properties:
   canonical_alias:
     type: string
+    format: mx-room-alias
+    pattern: "^#"
     description: The canonical alias of the room, if any.
     example: "#general:example.org"
   name:
@@ -29,6 +31,8 @@ properties:
     example: 42
   room_id:
     type: string
+    format: mx-room-id
+    pattern: "^!"
     description: The ID of the room.
     example: "!abcdefg:example.org"
   topic:
diff --git a/data/api/client-server/definitions/room_summary.yaml b/data/api/client-server/definitions/room_summary.yaml
index a8682e51..8499bac1 100644
--- a/data/api/client-server/definitions/room_summary.yaml
+++ b/data/api/client-server/definitions/room_summary.yaml
@@ -27,6 +27,8 @@ allOf:
         type: array
         items:
           type: string
+          format: mx-room-id
+          pattern: "^!"
         description: |-
           If the room is a [restricted room](/server-server-api/#restricted-rooms), these are the room IDs which
           are specified by the join rules. Empty or omitted otherwise.
diff --git a/data/api/client-server/room_summary.yaml b/data/api/client-server/room_summary.yaml
index 9d23c829..e5e241ed 100644
--- a/data/api/client-server/room_summary.yaml
+++ b/data/api/client-server/room_summary.yaml
@@ -46,7 +46,13 @@ paths:
           required: true
           example: "#monkeys:matrix.org"
           schema:
-            type: string
+            oneOf:
+              - type: string
+                format: mx-room-id
+                pattern: "^!"
+              - type: string
+                format: mx-room-alias
+                pattern: "^#"
         - in: query
           name: via
           description: |-
@@ -60,6 +66,7 @@ paths:
             type: array
             items:
               type: string
+              format: mx-server-name
       responses:
         "200":
           description: A summary of the room.