diff --git a/roomserver/api/query.go b/roomserver/api/query.go
index 3cb1b8a7b..9003a95a3 100644
--- a/roomserver/api/query.go
+++ b/roomserver/api/query.go
@@ -261,16 +261,6 @@ type QueryRoomVersionCapabilitiesResponse struct {
 	AvailableRoomVersions map[gomatrixserverlib.RoomVersion]string `json:"available"`
 }
 
-// QueryRoomVersionForRoom asks for the room version for a given room.
-type QueryRoomVersionForRoomRequest struct {
-	RoomID string `json:"room_id"`
-}
-
-// QueryRoomVersionCapabilitiesResponse is a response to QueryServersInRoomAtEventResponse
-type QueryRoomVersionForRoomResponse struct {
-	RoomVersion gomatrixserverlib.RoomVersion `json:"room_version"`
-}
-
 // RoomserverQueryAPI is used to query information from the room server.
 type RoomserverQueryAPI interface {
 	// Query the latest events and state for a room from the room server.
@@ -357,13 +347,6 @@ type RoomserverQueryAPI interface {
 		request *QueryRoomVersionCapabilitiesRequest,
 		response *QueryRoomVersionCapabilitiesResponse,
 	) error
-
-	// Asks for the room version for a given room.
-	QueryRoomVersionForRoom(
-		ctx context.Context,
-		request *QueryRoomVersionForRoomRequest,
-		response *QueryRoomVersionForRoomResponse,
-	) error
 }
 
 // RoomserverQueryLatestEventsAndStatePath is the HTTP path for the QueryLatestEventsAndState API.
@@ -402,9 +385,6 @@ const RoomserverQueryServersInRoomAtEventPath = "/api/roomserver/queryServersInR
 // RoomserverQueryRoomVersionCapabilitiesPath is the HTTP path for the QueryRoomVersionCapabilities API
 const RoomserverQueryRoomVersionCapabilitiesPath = "/api/roomserver/queryRoomVersionCapabilities"
 
-// RoomserverQueryRoomVersionCapabilitiesPath is the HTTP path for the QueryRoomVersionCapabilities API
-const RoomserverQueryRoomVersionForRoomPath = "/api/roomserver/queryRoomVersionForRoom"
-
 // NewRoomserverQueryAPIHTTP creates a RoomserverQueryAPI implemented by talking to a HTTP POST API.
 // If httpClient is nil then it uses the http.DefaultClient
 func NewRoomserverQueryAPIHTTP(roomserverURL string, httpClient *http.Client) RoomserverQueryAPI {
@@ -574,16 +554,3 @@ func (h *httpRoomserverQueryAPI) QueryRoomVersionCapabilities(
 	apiURL := h.roomserverURL + RoomserverQueryRoomVersionCapabilitiesPath
 	return commonHTTP.PostJSON(ctx, span, h.httpClient, apiURL, request, response)
 }
-
-// QueryRoomVersionForRoom implements RoomServerQueryAPI
-func (h *httpRoomserverQueryAPI) QueryRoomVersionForRoom(
-	ctx context.Context,
-	request *QueryRoomVersionForRoomRequest,
-	response *QueryRoomVersionForRoomResponse,
-) error {
-	span, ctx := opentracing.StartSpanFromContext(ctx, "QueryRoomVersionForRoom")
-	defer span.Finish()
-
-	apiURL := h.roomserverURL + RoomserverQueryRoomVersionForRoomPath
-	return commonHTTP.PostJSON(ctx, span, h.httpClient, apiURL, request, response)
-}
diff --git a/roomserver/query/query.go b/roomserver/query/query.go
index 01bbadb5b..f2e9e6155 100644
--- a/roomserver/query/query.go
+++ b/roomserver/query/query.go
@@ -804,20 +804,6 @@ func (r *RoomserverQueryAPI) QueryRoomVersionCapabilities(
 	return nil
 }
 
-// QueryRoomVersionCapabilities implements api.RoomserverQueryAPI
-func (r *RoomserverQueryAPI) QueryRoomVersionForRoom(
-	ctx context.Context,
-	request *api.QueryRoomVersionForRoomRequest,
-	response *api.QueryRoomVersionForRoomResponse,
-) error {
-	roomVersion, err := r.DB.GetRoomVersionForRoom(ctx, request.RoomID)
-	if err != nil {
-		return err
-	}
-	response.RoomVersion = roomVersion
-	return nil
-}
-
 // SetupHTTP adds the RoomserverQueryAPI handlers to the http.ServeMux.
 // nolint: gocyclo
 func (r *RoomserverQueryAPI) SetupHTTP(servMux *http.ServeMux) {
@@ -989,18 +975,4 @@ func (r *RoomserverQueryAPI) SetupHTTP(servMux *http.ServeMux) {
 			return util.JSONResponse{Code: http.StatusOK, JSON: &response}
 		}),
 	)
-	servMux.Handle(
-		api.RoomserverQueryRoomVersionForRoomPath,
-		common.MakeInternalAPI("QueryRoomVersionForRoom", func(req *http.Request) util.JSONResponse {
-			var request api.QueryRoomVersionForRoomRequest
-			var response api.QueryRoomVersionForRoomResponse
-			if err := json.NewDecoder(req.Body).Decode(&request); err != nil {
-				return util.ErrorResponse(err)
-			}
-			if err := r.QueryRoomVersionForRoom(req.Context(), &request, &response); err != nil {
-				return util.ErrorResponse(err)
-			}
-			return util.JSONResponse{Code: http.StatusOK, JSON: &response}
-		}),
-	)
 }
diff --git a/roomserver/version/version.go b/roomserver/version/version.go
index ed16ecca0..1ad502f23 100644
--- a/roomserver/version/version.go
+++ b/roomserver/version/version.go
@@ -43,11 +43,11 @@ var roomVersions = map[gomatrixserverlib.RoomVersion]RoomVersionDescription{
 		Stable:    true,
 	},
 	gomatrixserverlib.RoomVersionV3: RoomVersionDescription{
-		Supported: false,
+		Supported: true,
 		Stable:    false,
 	},
 	gomatrixserverlib.RoomVersionV4: RoomVersionDescription{
-		Supported: false,
+		Supported: true,
 		Stable:    false,
 	},
 	gomatrixserverlib.RoomVersionV5: RoomVersionDescription{
@@ -59,7 +59,7 @@ var roomVersions = map[gomatrixserverlib.RoomVersion]RoomVersionDescription{
 // DefaultRoomVersion contains the room version that will, by
 // default, be used to create new rooms on this server.
 func DefaultRoomVersion() gomatrixserverlib.RoomVersion {
-	return gomatrixserverlib.RoomVersionV2
+	return gomatrixserverlib.RoomVersionV4
 }
 
 // RoomVersions returns a map of all known room versions to this