diff --git a/spec/unit/embedded.spec.ts b/spec/unit/embedded.spec.ts
index e1e6f0513a1..b42acfff1df 100644
--- a/spec/unit/embedded.spec.ts
+++ b/spec/unit/embedded.spec.ts
@@ -75,6 +75,14 @@ class MockWidgetApi extends EventEmitter {
     public transport = { reply: jest.fn() };
 }
 
+declare module "../../src/types" {
+    interface StateEvents {
+        "org.example.foo": {
+            hello: string;
+        };
+    }
+}
+
 describe("RoomWidgetClient", () => {
     let widgetApi: MockedObject<WidgetApi>;
     let client: MatrixClient;
diff --git a/spec/unit/matrix-client.spec.ts b/spec/unit/matrix-client.spec.ts
index f80531f86bb..c87ab3177f3 100644
--- a/spec/unit/matrix-client.spec.ts
+++ b/spec/unit/matrix-client.spec.ts
@@ -38,30 +38,31 @@ import * as testUtils from "../test-utils/test-utils";
 import { makeBeaconInfoContent } from "../../src/content-helpers";
 import { M_BEACON_INFO } from "../../src/@types/beacon";
 import {
-    ContentHelpers,
     ClientPrefix,
+    ConditionKind,
+    ContentHelpers,
     Direction,
     EventTimeline,
+    EventTimelineSet,
+    getHttpUriForMxc,
     ICreateRoomOpts,
+    IPushRule,
     IRequestOpts,
     MatrixError,
     MatrixHttpApi,
     MatrixScheduler,
     Method,
-    Room,
-    EventTimelineSet,
     PushRuleActionName,
-    TweakName,
+    Room,
     RuleId,
-    IPushRule,
-    ConditionKind,
-    getHttpUriForMxc,
+    TweakName,
 } from "../../src";
 import { supportsMatrixCall } from "../../src/webrtc/call";
 import { makeBeaconEvent } from "../test-utils/beacon";
 import {
     IGNORE_INVITES_ACCOUNT_EVENT_KEY,
     POLICIES_ACCOUNT_EVENT_TYPE,
+    PolicyRecommendation,
     PolicyScope,
 } from "../../src/models/invites-ignorer";
 import { IOlmDevice } from "../../src/crypto/algorithms/megolm";
@@ -2082,10 +2083,10 @@ describe("MatrixClient", function () {
             await client.ignoredInvites.addSource(NEW_SOURCE_ROOM_ID);
 
             // Add a rule in the new source room.
-            await client.sendStateEvent(NEW_SOURCE_ROOM_ID, PolicyScope.User, {
+            await client.sendStateEvent(NEW_SOURCE_ROOM_ID, EventType.PolicyRuleUser, {
                 entity: "*:example.org",
                 reason: "just a test",
-                recommendation: "m.ban",
+                recommendation: PolicyRecommendation.Ban,
             });
 
             // We should reject this invite.
@@ -2172,8 +2173,8 @@ describe("MatrixClient", function () {
             // Check where it shows up.
             const targetRoomId = ignoreInvites2.target;
             const targetRoom = client.getRoom(targetRoomId) as WrappedRoom;
-            expect(targetRoom._state.get(PolicyScope.User)[eventId]).toBeTruthy();
-            expect(newSourceRoom._state.get(PolicyScope.User)?.[eventId]).toBeFalsy();
+            expect(targetRoom._state.get(EventType.PolicyRuleUser)[eventId]).toBeTruthy();
+            expect(newSourceRoom._state.get(EventType.PolicyRuleUser)?.[eventId]).toBeFalsy();
         });
     });
 
diff --git a/src/@types/common.ts b/src/@types/common.ts
index 77b856faf93..fc8e7af7328 100644
--- a/src/@types/common.ts
+++ b/src/@types/common.ts
@@ -15,3 +15,8 @@ limitations under the License.
 */
 
 export type NonEmptyArray<T> = [T, ...T[]];
+
+// Based on https://stackoverflow.com/a/53229857/3532235
+export type Without<T, U> = { [P in Exclude<keyof T, keyof U>]?: never };
+export type XOR<T, U> = T | U extends object ? (Without<T, U> & U) | (Without<U, T> & T) : T | U;
+export type Writeable<T> = { -readonly [P in keyof T]: T[P] };
diff --git a/src/@types/event.ts b/src/@types/event.ts
index caa87f9f82e..a6dafcfa1b9 100644
--- a/src/@types/event.ts
+++ b/src/@types/event.ts
@@ -15,6 +15,34 @@ limitations under the License.
 */
 
 import { UnstableValue } from "../NamespacedValue";
+import {
+    PolicyRuleEventContent,
+    RoomAvatarEventContent,
+    RoomCanonicalAliasEventContent,
+    RoomCreateEventContent,
+    RoomEncryptionEventContent,
+    RoomGuestAccessEventContent,
+    RoomHistoryVisibilityEventContent,
+    RoomJoinRulesEventContent,
+    RoomMemberEventContent,
+    RoomNameEventContent,
+    RoomPinnedEventsEventContent,
+    RoomPowerLevelsEventContent,
+    RoomServerAclEventContent,
+    RoomThirdPartyInviteEventContent,
+    RoomTombstoneEventContent,
+    RoomTopicEventContent,
+    SpaceChildEventContent,
+    SpaceParentEventContent,
+} from "./state_events";
+import {
+    ExperimentalGroupCallRoomMemberState,
+    IGroupCallRoomMemberState,
+    IGroupCallRoomState,
+} from "../webrtc/groupCall";
+import { MSC3089EventContent } from "../models/MSC3089Branch";
+import { M_BEACON_INFO, MBeaconInfoEventContent } from "./beacon";
+import { XOR } from "./common";
 
 export enum EventType {
     // Room state events
@@ -35,6 +63,11 @@ export enum EventType {
     RoomTombstone = "m.room.tombstone",
     RoomPredecessor = "org.matrix.msc3946.room_predecessor",
 
+    // Moderation policy lists
+    PolicyRuleUser = "m.policy.rule.user",
+    PolicyRuleRoom = "m.policy.rule.room",
+    PolicyRuleServer = "m.policy.rule.server",
+
     SpaceChild = "m.space.child",
     SpaceParent = "m.space.parent",
 
@@ -260,3 +293,38 @@ export interface IEncryptedFile {
     hashes: { [alg: string]: string };
     v: string;
 }
+
+export interface StateEvents {
+    [EventType.RoomCanonicalAlias]: RoomCanonicalAliasEventContent;
+    [EventType.RoomCreate]: RoomCreateEventContent;
+    [EventType.RoomJoinRules]: RoomJoinRulesEventContent;
+    [EventType.RoomMember]: RoomMemberEventContent;
+    // XXX: Spec says this event has 3 required fields but kicking such an invitation requires sending `{}`
+    [EventType.RoomThirdPartyInvite]: XOR<RoomThirdPartyInviteEventContent, {}>;
+    [EventType.RoomPowerLevels]: RoomPowerLevelsEventContent;
+    [EventType.RoomName]: RoomNameEventContent;
+    [EventType.RoomTopic]: RoomTopicEventContent;
+    [EventType.RoomAvatar]: RoomAvatarEventContent;
+    [EventType.RoomPinnedEvents]: RoomPinnedEventsEventContent;
+    [EventType.RoomEncryption]: RoomEncryptionEventContent;
+    [EventType.RoomHistoryVisibility]: RoomHistoryVisibilityEventContent;
+    [EventType.RoomGuestAccess]: RoomGuestAccessEventContent;
+    [EventType.RoomServerAcl]: RoomServerAclEventContent;
+    [EventType.RoomTombstone]: RoomTombstoneEventContent;
+    [EventType.SpaceChild]: SpaceChildEventContent;
+    [EventType.SpaceParent]: SpaceParentEventContent;
+
+    [EventType.PolicyRuleUser]: XOR<PolicyRuleEventContent, {}>;
+    [EventType.PolicyRuleRoom]: XOR<PolicyRuleEventContent, {}>;
+    [EventType.PolicyRuleServer]: XOR<PolicyRuleEventContent, {}>;
+
+    // MSC3401
+    [EventType.GroupCallPrefix]: IGroupCallRoomState;
+    [EventType.GroupCallMemberPrefix]: XOR<IGroupCallRoomMemberState, ExperimentalGroupCallRoomMemberState>;
+
+    // MSC3089
+    [UNSTABLE_MSC3089_BRANCH.name]: MSC3089EventContent;
+
+    // MSC3672
+    [M_BEACON_INFO.name]: MBeaconInfoEventContent;
+}
diff --git a/src/@types/partials.ts b/src/@types/partials.ts
index 49f92f32759..6aaea79963e 100644
--- a/src/@types/partials.ts
+++ b/src/@types/partials.ts
@@ -14,19 +14,12 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-export interface IImageInfo {
-    size?: number;
-    mimetype?: string;
-    thumbnail_info?: {
-        // eslint-disable-line camelcase
-        w?: number;
-        h?: number;
-        size?: number;
-        mimetype?: string;
-    };
-    w?: number;
-    h?: number;
-}
+import { ImageInfo } from "./media";
+
+/**
+ * @deprecated use {@link ImageInfo} instead.
+ */
+export type IImageInfo = ImageInfo;
 
 export enum Visibility {
     Public = "public",
diff --git a/src/@types/state_events.ts b/src/@types/state_events.ts
new file mode 100644
index 00000000000..0e077a9e47f
--- /dev/null
+++ b/src/@types/state_events.ts
@@ -0,0 +1,144 @@
+/*
+Copyright 2024 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { RoomType } from "./event";
+import { GuestAccess, HistoryVisibility, RestrictedAllowType } from "./partials";
+import { ImageInfo } from "./media";
+import { PolicyRecommendation } from "../models/invites-ignorer";
+
+export interface RoomCanonicalAliasEventContent {
+    alias?: string;
+    alt_aliases?: string[];
+}
+
+export interface RoomCreateEventContent {
+    "creator"?: string;
+    "m.federate"?: boolean;
+    "predecessor"?: {
+        event_id: string;
+        room_id: string;
+    };
+    "room_version"?: string;
+    "type"?: RoomType;
+}
+
+export interface RoomJoinRulesEventContent {
+    allow?: {
+        room_id: string;
+        type: RestrictedAllowType;
+    }[];
+}
+
+export interface RoomMemberEventContent {
+    avatar_url?: string;
+    displayname?: string;
+    is_direct?: boolean;
+    join_authorised_via_users_server?: string;
+    membership: "invite" | "join" | "knock" | "leave" | "ban";
+    reason?: string;
+    third_party_invite?: {
+        display_name: string;
+        signed: {
+            mxid: string;
+            token: string;
+            ts: number;
+        };
+    };
+}
+
+export interface RoomThirdPartyInviteEventContent {
+    display_name: string;
+    key_validity_url: string;
+    public_key: string;
+    public_keys: {
+        key_validity_url?: string;
+        public_key: string;
+    }[];
+}
+
+export interface RoomPowerLevelsEventContent {
+    ban?: number;
+    events?: { [eventType: string]: number };
+    events_default?: number;
+    invite?: number;
+    kick?: number;
+    notifications?: {
+        room?: number;
+    };
+    redact?: number;
+    state_default?: number;
+    users?: { [userId: string]: number };
+    users_default?: number;
+}
+
+export interface RoomNameEventContent {
+    name: string;
+}
+
+export interface RoomTopicEventContent {
+    topic: string;
+}
+
+export interface RoomAvatarEventContent {
+    url?: string;
+    info?: ImageInfo;
+}
+
+export interface RoomPinnedEventsEventContent {
+    pinned: string[];
+}
+
+export interface RoomEncryptionEventContent {
+    algorithm: "m.megolm.v1.aes-sha2";
+    rotation_period_ms?: number;
+    rotation_period_msgs?: number;
+}
+
+export interface RoomHistoryVisibilityEventContent {
+    history_visibility: HistoryVisibility;
+}
+
+export interface RoomGuestAccessEventContent {
+    guest_access: GuestAccess;
+}
+
+export interface RoomServerAclEventContent {
+    allow?: string[];
+    allow_ip_literals?: boolean;
+    deny?: string[];
+}
+
+export interface RoomTombstoneEventContent {
+    body: string;
+    replacement_room: string;
+}
+
+export interface SpaceChildEventContent {
+    order?: string;
+    suggested?: boolean;
+    via?: string[];
+}
+
+export interface SpaceParentEventContent {
+    canonical?: boolean;
+    via?: string[];
+}
+
+export interface PolicyRuleEventContent {
+    entity: string;
+    reason: string;
+    recommendation: PolicyRecommendation;
+}
diff --git a/src/client.ts b/src/client.ts
index 56ec1030cd6..0233749ae8c 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -35,14 +35,14 @@ import {
 import { StubStore } from "./store/stub";
 import { CallEvent, CallEventHandlerMap, createNewMatrixCall, MatrixCall, supportsMatrixCall } from "./webrtc/call";
 import { Filter, IFilterDefinition, IRoomEventFilter } from "./filter";
-import { CallEventHandlerEvent, CallEventHandler, CallEventHandlerEventHandlerMap } from "./webrtc/callEventHandler";
+import { CallEventHandler, CallEventHandlerEvent, CallEventHandlerEventHandlerMap } from "./webrtc/callEventHandler";
 import {
     GroupCallEventHandler,
     GroupCallEventHandlerEvent,
     GroupCallEventHandlerEventHandlerMap,
 } from "./webrtc/groupCallEventHandler";
 import * as utils from "./utils";
-import { replaceParam, QueryDict, sleep, noUnsafeEventProps, safeSet } from "./utils";
+import { noUnsafeEventProps, QueryDict, replaceParam, safeSet, sleep } from "./utils";
 import { Direction, EventTimeline } from "./models/event-timeline";
 import { IActionsObject, PushProcessor } from "./pushprocessor";
 import { AutoDiscovery, AutoDiscoveryAction } from "./autodiscovery";
@@ -64,12 +64,12 @@ import {
     IdentityPrefix,
     IHttpOpts,
     IRequestOpts,
-    TokenRefreshFunction,
     MatrixError,
     MatrixHttpApi,
     MediaPrefix,
     Method,
     retryNetworkOperation,
+    TokenRefreshFunction,
     Upload,
     UploadOpts,
     UploadResponse,
@@ -145,11 +145,20 @@ import {
     RelationType,
     RoomCreateTypeField,
     RoomType,
+    StateEvents,
     UNSTABLE_MSC3088_ENABLED,
     UNSTABLE_MSC3088_PURPOSE,
     UNSTABLE_MSC3089_TREE_SUBTYPE,
 } from "./@types/event";
-import { IdServerUnbindResult, IImageInfo, JoinRule, Preset, Visibility } from "./@types/partials";
+import {
+    GuestAccess,
+    HistoryVisibility,
+    IdServerUnbindResult,
+    IImageInfo,
+    JoinRule,
+    Preset,
+    Visibility,
+} from "./@types/partials";
 import { EventMapper, eventMapperFor, MapperOpts } from "./event-mapper";
 import { randomString } from "./randomstring";
 import { BackupManager, IKeyBackup, IKeyBackupCheck, IPreparedKeyBackupVersion, TrustInfo } from "./crypto/backup";
@@ -6704,7 +6713,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
             roomId,
             EventType.RoomGuestAccess,
             {
-                guest_access: opts.allowJoin ? "can_join" : "forbidden",
+                guest_access: opts.allowJoin ? GuestAccess.CanJoin : GuestAccess.Forbidden,
             },
             "",
         );
@@ -6715,7 +6724,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
                 roomId,
                 EventType.RoomHistoryVisibility,
                 {
-                    history_visibility: "world_readable",
+                    history_visibility: HistoryVisibility.WorldReadable,
                 },
                 "",
             );
@@ -8386,14 +8395,19 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
     }
 
     /**
+     * Send a state event into a room
+     * @param roomId - ID of the room to send the event into
+     * @param eventType - type of the state event to send
+     * @param content - content of the event to send
+     * @param stateKey - the stateKey to send into the room
      * @param opts - Options for the request function.
      * @returns Promise which resolves: TODO
      * @returns Rejects: with an error response.
      */
-    public sendStateEvent(
+    public sendStateEvent<K extends keyof StateEvents>(
         roomId: string,
-        eventType: string,
-        content: IContent,
+        eventType: K,
+        content: StateEvents[K],
         stateKey = "",
         opts: IRequestOpts = {},
     ): Promise<ISendEventResponse> {
@@ -8406,7 +8420,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         if (stateKey !== undefined) {
             path = utils.encodeUri(path + "/$stateKey", pathParams);
         }
-        return this.http.authedRequest(Method.Put, path, undefined, content, opts);
+        return this.http.authedRequest(Method.Put, path, undefined, content as Body, opts);
     }
 
     /**
diff --git a/src/models/MSC3089Branch.ts b/src/models/MSC3089Branch.ts
index e21482ac54d..3a294ebc297 100644
--- a/src/models/MSC3089Branch.ts
+++ b/src/models/MSC3089Branch.ts
@@ -22,6 +22,13 @@ import { EventTimeline } from "./event-timeline";
 import { FileType } from "../http-api";
 import type { ISendEventResponse } from "../@types/requests";
 
+export interface MSC3089EventContent {
+    active?: boolean;
+    name?: string;
+    locked?: boolean;
+    version?: number;
+}
+
 /**
  * Represents a [MSC3089](https://github.com/matrix-org/matrix-doc/pull/3089) branch - a reference
  * to a file (leaf) in the tree. Note that this is UNSTABLE and subject to breaking changes
diff --git a/src/models/MSC3089TreeSpace.ts b/src/models/MSC3089TreeSpace.ts
index 198e8d3166f..3890afeb77e 100644
--- a/src/models/MSC3089TreeSpace.ts
+++ b/src/models/MSC3089TreeSpace.ts
@@ -34,6 +34,7 @@ import { isRoomSharedHistory } from "../crypto/algorithms/megolm";
 import { ISendEventResponse } from "../@types/requests";
 import { FileType } from "../http-api";
 import { KnownMembership } from "../@types/membership";
+import { RoomPowerLevelsEventContent, SpaceChildEventContent } from "../@types/state_events";
 
 /**
  * The recommended defaults for a tree space's power levels. Note that this
@@ -176,7 +177,7 @@ export class MSC3089TreeSpace {
         const currentPls = this.room.currentState.getStateEvents(EventType.RoomPowerLevels, "");
         if (Array.isArray(currentPls)) throw new Error("Unexpected return type for power levels");
 
-        const pls = currentPls?.getContent() || {};
+        const pls = currentPls?.getContent<RoomPowerLevelsEventContent>() || {};
         const viewLevel = pls["users_default"] || 0;
         const editLevel = pls["events_default"] || 50;
         const adminLevel = pls["events"]?.[EventType.RoomPowerLevels] || 100;
@@ -234,7 +235,7 @@ export class MSC3089TreeSpace {
             this.roomId,
             EventType.SpaceChild,
             {
-                via: [this.client.getDomain()],
+                via: [this.client.getDomain()!],
             },
             directory.roomId,
         );
@@ -243,7 +244,7 @@ export class MSC3089TreeSpace {
             directory.roomId,
             EventType.SpaceParent,
             {
-                via: [this.client.getDomain()],
+                via: [this.client.getDomain()!],
             },
             this.roomId,
         );
@@ -450,7 +451,9 @@ export class MSC3089TreeSpace {
                     // XXX: We should be creating gaps to avoid conflicts
                     lastOrder = lastOrder ? nextString(lastOrder) : DEFAULT_ALPHABET[0];
                     const currentChild = parentRoom.currentState.getStateEvents(EventType.SpaceChild, target.roomId);
-                    const content = currentChild?.getContent() ?? { via: [this.client.getDomain()] };
+                    const content = currentChild?.getContent<SpaceChildEventContent>() ?? {
+                        via: [this.client.getDomain()!],
+                    };
                     await this.client.sendStateEvent(
                         parentRoom.roomId,
                         EventType.SpaceChild,
@@ -473,7 +476,7 @@ export class MSC3089TreeSpace {
 
         // Now we can finally update our own order state
         const currentChild = parentRoom.currentState.getStateEvents(EventType.SpaceChild, this.roomId);
-        const content = currentChild?.getContent() ?? { via: [this.client.getDomain()] };
+        const content = currentChild?.getContent<SpaceChildEventContent>() ?? { via: [this.client.getDomain()!] };
         await this.client.sendStateEvent(
             parentRoom.roomId,
             EventType.SpaceChild,
diff --git a/src/models/invites-ignorer.ts b/src/models/invites-ignorer.ts
index 026c4a2bbad..a76d6a83a57 100644
--- a/src/models/invites-ignorer.ts
+++ b/src/models/invites-ignorer.ts
@@ -22,6 +22,7 @@ import { EventTimeline } from "./event-timeline";
 import { Preset } from "../@types/partials";
 import { globToRegexp } from "../utils";
 import { Room } from "./room";
+import { EventType, StateEvents } from "../@types/event";
 
 /// The event type storing the user's individual policies.
 ///
@@ -37,7 +38,7 @@ export const IGNORE_INVITES_ACCOUNT_EVENT_KEY = new UnstableValue(
 );
 
 /// The types of recommendations understood.
-enum PolicyRecommendation {
+export enum PolicyRecommendation {
     Ban = "m.ban",
 }
 
@@ -64,6 +65,12 @@ export enum PolicyScope {
     Server = "m.policy.server",
 }
 
+const scopeToEventTypeMap: Record<PolicyScope, keyof StateEvents> = {
+    [PolicyScope.User]: EventType.PolicyRuleUser,
+    [PolicyScope.Room]: EventType.PolicyRuleRoom,
+    [PolicyScope.Server]: EventType.PolicyRuleServer,
+};
+
 /**
  * A container for ignored invites.
  *
@@ -87,7 +94,7 @@ export class IgnoredInvites {
      */
     public async addRule(scope: PolicyScope, entity: string, reason: string): Promise<string> {
         const target = await this.getOrCreateTargetRoom();
-        const response = await this.client.sendStateEvent(target.roomId, scope, {
+        const response = await this.client.sendStateEvent(target.roomId, scopeToEventTypeMap[scope], {
             entity,
             reason,
             recommendation: PolicyRecommendation.Ban,
@@ -173,7 +180,7 @@ export class IgnoredInvites {
                 { scope: PolicyScope.User, entities: [sender] },
                 { scope: PolicyScope.Server, entities: [senderServer, roomServer] },
             ]) {
-                const events = state.getStateEvents(scope);
+                const events = state.getStateEvents(scopeToEventTypeMap[scope]);
                 for (const event of events) {
                     const content = event.getContent();
                     if (content?.recommendation != PolicyRecommendation.Ban) {
diff --git a/src/types.ts b/src/types.ts
index 1edb3979564..97a89002c99 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -23,3 +23,5 @@ limitations under the License.
 
 export type * from "./@types/media";
 export * from "./@types/membership";
+export type * from "./@types/event";
+export type * from "./@types/state_events";
diff --git a/src/webrtc/groupCall.ts b/src/webrtc/groupCall.ts
index e5711986894..a33f676b1b7 100644
--- a/src/webrtc/groupCall.ts
+++ b/src/webrtc/groupCall.ts
@@ -35,6 +35,7 @@ import {
 import { SummaryStatsReportGatherer } from "./stats/summaryStatsReportGatherer";
 import { CallFeedStatsReporter } from "./stats/callFeedStatsReporter";
 import { KnownMembership } from "../@types/membership";
+import { CallMembershipData } from "../matrixrtc/CallMembership";
 
 export enum GroupCallIntent {
     Ring = "m.ring",
@@ -167,6 +168,7 @@ export interface IGroupCallDataChannelOptions {
 export interface IGroupCallRoomState {
     "m.intent": GroupCallIntent;
     "m.type": GroupCallType;
+    "m.terminated"?: GroupCallTerminationReason;
     "io.element.ptt"?: boolean;
     // TODO: Specify data-channels
     "dataChannelsEnabled"?: boolean;
@@ -196,6 +198,11 @@ export interface IGroupCallRoomMemberState {
     "m.calls": IGroupCallRoomMemberCallState[];
 }
 
+// XXX: this hasn't made it into the MSC yet
+export interface ExperimentalGroupCallRoomMemberState {
+    memberships: CallMembershipData[];
+}
+
 export enum GroupCallState {
     LocalCallFeedUninitialized = "local_call_feed_uninitialized",
     InitializingLocalCallFeed = "initializing_local_call_feed",