diff --git a/federationapi/internal/perform.go b/federationapi/internal/perform.go
index 08287c692..c580e5275 100644
--- a/federationapi/internal/perform.go
+++ b/federationapi/internal/perform.go
@@ -256,10 +256,10 @@ func (r *FederationInternalAPI) performJoinUsingServer(
 	// waste the effort.
 	// TODO: Can we expand Check here to return a list of missing auth
 	// events rather than failing one at a time?
-	var respState *fclient.RespState
-	respState, err = respSendJoin.Check(
+	var respState gomatrixserverlib.StateResponse
+	respState, err = gomatrixserverlib.CheckSendJoinResponse(
 		context.Background(),
-		respMakeJoin.RoomVersion,
+		respMakeJoin.RoomVersion, &respSendJoin,
 		r.keyRing,
 		event,
 		federatedAuthProvider(ctx, r.federation, r.keyRing, origin, serverName),
@@ -274,7 +274,7 @@ func (r *FederationInternalAPI) performJoinUsingServer(
 	// joining a room, waiting for 200 OK then changing device keys and have those keys not be sent
 	// to other servers (this was a cause of a flakey sytest "Local device key changes get to remote servers")
 	// The events are trusted now as we performed auth checks above.
-	joinedHosts, err := consumers.JoinedHostsFromEvents(respState.StateEvents.TrustedEvents(respMakeJoin.RoomVersion, false))
+	joinedHosts, err := consumers.JoinedHostsFromEvents(respState.GetStateEvents().TrustedEvents(respMakeJoin.RoomVersion, false))
 	if err != nil {
 		return fmt.Errorf("JoinedHostsFromEvents: failed to get joined hosts: %s", err)
 	}
@@ -469,11 +469,12 @@ func (r *FederationInternalAPI) performOutboundPeekUsingServer(
 
 	// we have the peek state now so let's process regardless of whether upstream gives up
 	ctx = context.Background()
-	respState := respPeek.ToRespState()
 
 	// authenticate the state returned (check its auth events etc)
 	// the equivalent of CheckSendJoinResponse()
-	authEvents, _, err := respState.Check(ctx, respPeek.RoomVersion, r.keyRing, federatedAuthProvider(ctx, r.federation, r.keyRing, r.cfg.Matrix.ServerName, serverName))
+	authEvents, stateEvents, err := gomatrixserverlib.CheckStateResponse(
+		ctx, &respPeek, respPeek.RoomVersion, r.keyRing, federatedAuthProvider(ctx, r.federation, r.keyRing, r.cfg.Matrix.ServerName, serverName),
+	)
 	if err != nil {
 		return fmt.Errorf("error checking state returned from peeking: %w", err)
 	}
@@ -497,7 +498,11 @@ func (r *FederationInternalAPI) performOutboundPeekUsingServer(
 	if err = roomserverAPI.SendEventWithState(
 		ctx, r.rsAPI, r.cfg.Matrix.ServerName,
 		roomserverAPI.KindNew,
-		&respState,
+		// use the authorized state from CheckStateResponse
+		&fclient.RespState{
+			StateEvents: gomatrixserverlib.NewEventJSONsFromEvents(stateEvents),
+			AuthEvents:  gomatrixserverlib.NewEventJSONsFromEvents(authEvents),
+		},
 		respPeek.LatestEvent.Headered(respPeek.RoomVersion),
 		serverName,
 		nil,
diff --git a/go.mod b/go.mod
index 6d1817024..b48489095 100644
--- a/go.mod
+++ b/go.mod
@@ -22,7 +22,7 @@ require (
 	github.com/matrix-org/dugong v0.0.0-20210921133753-66e6b1c67e2e
 	github.com/matrix-org/go-sqlite3-js v0.0.0-20220419092513-28aa791a1c91
 	github.com/matrix-org/gomatrix v0.0.0-20220926102614-ceba4d9f7530
-	github.com/matrix-org/gomatrixserverlib v0.0.0-20230405171344-5f597d85ba4f
+	github.com/matrix-org/gomatrixserverlib v0.0.0-20230414110520-bcb28309fbcf
 	github.com/matrix-org/pinecone v0.11.1-0.20230210171230-8c3b24f2649a
 	github.com/matrix-org/util v0.0.0-20221111132719-399730281e66
 	github.com/mattn/go-sqlite3 v1.14.16
diff --git a/go.sum b/go.sum
index fffe51b18..dd9669794 100644
--- a/go.sum
+++ b/go.sum
@@ -325,6 +325,12 @@ github.com/matrix-org/gomatrixserverlib v0.0.0-20230320105331-4dd7ff2f0e3a h1:F6
 github.com/matrix-org/gomatrixserverlib v0.0.0-20230320105331-4dd7ff2f0e3a/go.mod h1:7HTbSZe+CIdmeqVyFMekwD5dFU8khWQyngKATvd12FU=
 github.com/matrix-org/gomatrixserverlib v0.0.0-20230405171344-5f597d85ba4f h1:D7IgZA2DxBroqCTxo2uXEmjj8eCI1OzqqKRE4SAgmBU=
 github.com/matrix-org/gomatrixserverlib v0.0.0-20230405171344-5f597d85ba4f/go.mod h1:7HTbSZe+CIdmeqVyFMekwD5dFU8khWQyngKATvd12FU=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20230406115722-88763372cbd9 h1:bnIeD+u46GkPzfBcH9Su4sUBRZ9jqHcKER8hmaNnGD8=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20230406115722-88763372cbd9/go.mod h1:7HTbSZe+CIdmeqVyFMekwD5dFU8khWQyngKATvd12FU=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20230406130834-e85c3bfeed05 h1:s4JL2PPTgB6pR1ouDwq6KpqmV5hUTAP+HB1ajlemHWA=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20230406130834-e85c3bfeed05/go.mod h1:7HTbSZe+CIdmeqVyFMekwD5dFU8khWQyngKATvd12FU=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20230414110520-bcb28309fbcf h1:bfjLsvf1M7IFJuwmFJAsgUi4XaaHs07e6tub0tb3Fpw=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20230414110520-bcb28309fbcf/go.mod h1:7HTbSZe+CIdmeqVyFMekwD5dFU8khWQyngKATvd12FU=
 github.com/matrix-org/pinecone v0.11.1-0.20230210171230-8c3b24f2649a h1:awrPDf9LEFySxTLKYBMCiObelNx/cBuv/wzllvCCH3A=
 github.com/matrix-org/pinecone v0.11.1-0.20230210171230-8c3b24f2649a/go.mod h1:HchJX9oKMXaT2xYFs0Ha/6Zs06mxLU8k6F1ODnrGkeQ=
 github.com/matrix-org/util v0.0.0-20221111132719-399730281e66 h1:6z4KxomXSIGWqhHcfzExgkH3Z3UkIXry4ibJS4Aqz2Y=
diff --git a/roomserver/api/wrapper.go b/roomserver/api/wrapper.go
index 5f74c7854..831ffe25c 100644
--- a/roomserver/api/wrapper.go
+++ b/roomserver/api/wrapper.go
@@ -50,10 +50,10 @@ func SendEvents(
 func SendEventWithState(
 	ctx context.Context, rsAPI InputRoomEventsAPI,
 	virtualHost gomatrixserverlib.ServerName, kind Kind,
-	state *fclient.RespState, event *gomatrixserverlib.HeaderedEvent,
+	state gomatrixserverlib.StateResponse, event *gomatrixserverlib.HeaderedEvent,
 	origin gomatrixserverlib.ServerName, haveEventIDs map[string]bool, async bool,
 ) error {
-	outliers := state.Events(event.RoomVersion)
+	outliers := gomatrixserverlib.LineariseStateResponse(event.RoomVersion, state)
 	ires := make([]InputRoomEvent, 0, len(outliers))
 	for _, outlier := range outliers {
 		if haveEventIDs[outlier.EventID()] {
@@ -66,7 +66,7 @@ func SendEventWithState(
 		})
 	}
 
-	stateEvents := state.StateEvents.UntrustedEvents(event.RoomVersion)
+	stateEvents := state.GetStateEvents().UntrustedEvents(event.RoomVersion)
 	stateEventIDs := make([]string, len(stateEvents))
 	for i := range stateEvents {
 		stateEventIDs[i] = stateEvents[i].EventID()
diff --git a/roomserver/internal/input/input_missing.go b/roomserver/internal/input/input_missing.go
index 74b138741..16bc18d8b 100644
--- a/roomserver/internal/input/input_missing.go
+++ b/roomserver/internal/input/input_missing.go
@@ -641,31 +641,19 @@ func (t *missingStateReq) lookupMissingStateViaState(
 	if err != nil {
 		return nil, err
 	}
-	s := fclient.RespState{
+
+	// Check that the returned state is valid.
+	authEvents, stateEvents, err := gomatrixserverlib.CheckStateResponse(ctx, &fclient.RespState{
 		StateEvents: state.GetStateEvents(),
 		AuthEvents:  state.GetAuthEvents(),
-	}
-	// Check that the returned state is valid.
-	authEvents, stateEvents, err := s.Check(ctx, roomVersion, t.keys, nil)
+	}, roomVersion, t.keys, nil)
 	if err != nil {
 		return nil, err
 	}
-	parsedState := &parsedRespState{
+	return &parsedRespState{
 		AuthEvents:  authEvents,
 		StateEvents: stateEvents,
-	}
-	// Cache the results of this state lookup and deduplicate anything we already
-	// have in the cache, freeing up memory.
-	// We load these as trusted as we called state.Check before which loaded them as untrusted.
-	for i, evJSON := range s.AuthEvents {
-		ev, _ := gomatrixserverlib.NewEventFromTrustedJSON(evJSON, false, roomVersion)
-		parsedState.AuthEvents[i] = t.cacheAndReturn(ev)
-	}
-	for i, evJSON := range s.StateEvents {
-		ev, _ := gomatrixserverlib.NewEventFromTrustedJSON(evJSON, false, roomVersion)
-		parsedState.StateEvents[i] = t.cacheAndReturn(ev)
-	}
-	return parsedState, nil
+	}, nil
 }
 
 func (t *missingStateReq) lookupMissingStateViaStateIDs(ctx context.Context, roomID, eventID string, roomVersion gomatrixserverlib.RoomVersion) (
diff --git a/setup/mscs/msc2836/msc2836.go b/setup/mscs/msc2836/msc2836.go
index e1758920b..a12a28b18 100644
--- a/setup/mscs/msc2836/msc2836.go
+++ b/setup/mscs/msc2836/msc2836.go
@@ -654,11 +654,11 @@ func (rc *reqCtx) injectResponseToRoomserver(res *MSC2836EventRelationshipsRespo
 			messageEvents = append(messageEvents, ev)
 		}
 	}
-	respState := fclient.RespState{
+	respState := &fclient.RespState{
 		AuthEvents:  res.AuthChain,
 		StateEvents: stateEvents,
 	}
-	eventsInOrder := respState.Events(rc.roomVersion)
+	eventsInOrder := gomatrixserverlib.LineariseStateResponse(rc.roomVersion, respState)
 	// everything gets sent as an outlier because auth chain events may be disjoint from the DAG
 	// as may the threaded events.
 	var ires []roomserver.InputRoomEvent