diff --git a/spec/unit/matrixrtc/CallMembership.spec.ts b/spec/unit/matrixrtc/CallMembership.spec.ts
index 3d259103cc5..bf6ded10abf 100644
--- a/spec/unit/matrixrtc/CallMembership.spec.ts
+++ b/spec/unit/matrixrtc/CallMembership.spec.ts
@@ -15,16 +15,7 @@ limitations under the License.
 */
 
 import { MatrixEvent } from "../../../src";
-import { CallMembership, CallMembershipData } from "../../../src/matrixrtc/CallMembership";
-
-const membershipTemplate: CallMembershipData = {
-    call_id: "",
-    scope: "m.room",
-    application: "m.call",
-    device_id: "AAAAAAA",
-    expires: 5000,
-    membershipID: "bloop",
-};
+import { CallMembership, CallMembershipDataLegacy, SessionMembershipData } from "../../../src/matrixrtc/CallMembership";
 
 function makeMockEvent(originTs = 0): MatrixEvent {
     return {
@@ -34,96 +25,175 @@ function makeMockEvent(originTs = 0): MatrixEvent {
 }
 
 describe("CallMembership", () => {
-    it("rejects membership with no expiry and no expires_ts", () => {
-        expect(() => {
-            new CallMembership(
-                makeMockEvent(),
-                Object.assign({}, membershipTemplate, { expires: undefined, expires_ts: undefined }),
+    describe("CallMembershipDataLegacy", () => {
+        const membershipTemplate: CallMembershipDataLegacy = {
+            call_id: "",
+            scope: "m.room",
+            application: "m.call",
+            device_id: "AAAAAAA",
+            expires: 5000,
+            membershipID: "bloop",
+            foci_active: [{ type: "livekit" }],
+        };
+        it("rejects membership with no expiry and no expires_ts", () => {
+            expect(() => {
+                new CallMembership(
+                    makeMockEvent(),
+                    Object.assign({}, membershipTemplate, { expires: undefined, expires_ts: undefined }),
+                );
+            }).toThrow();
+        });
+
+        it("rejects membership with no device_id", () => {
+            expect(() => {
+                new CallMembership(makeMockEvent(), Object.assign({}, membershipTemplate, { device_id: undefined }));
+            }).toThrow();
+        });
+
+        it("rejects membership with no call_id", () => {
+            expect(() => {
+                new CallMembership(makeMockEvent(), Object.assign({}, membershipTemplate, { call_id: undefined }));
+            }).toThrow();
+        });
+
+        it("allow membership with no scope", () => {
+            expect(() => {
+                new CallMembership(makeMockEvent(), Object.assign({}, membershipTemplate, { scope: undefined }));
+            }).not.toThrow();
+        });
+        it("rejects with malformatted expires_ts", () => {
+            expect(() => {
+                new CallMembership(makeMockEvent(), Object.assign({}, membershipTemplate, { expires_ts: "string" }));
+            }).toThrow();
+        });
+        it("rejects with malformatted expires", () => {
+            expect(() => {
+                new CallMembership(makeMockEvent(), Object.assign({}, membershipTemplate, { expires: "string" }));
+            }).toThrow();
+        });
+
+        it("uses event timestamp if no created_ts", () => {
+            const membership = new CallMembership(makeMockEvent(12345), membershipTemplate);
+            expect(membership.createdTs()).toEqual(12345);
+        });
+
+        it("uses created_ts if present", () => {
+            const membership = new CallMembership(
+                makeMockEvent(12345),
+                Object.assign({}, membershipTemplate, { created_ts: 67890 }),
             );
-        }).toThrow();
-    });
+            expect(membership.createdTs()).toEqual(67890);
+        });
 
-    it("rejects membership with no device_id", () => {
-        expect(() => {
-            new CallMembership(makeMockEvent(), Object.assign({}, membershipTemplate, { device_id: undefined }));
-        }).toThrow();
-    });
+        it("computes absolute expiry time based on expires", () => {
+            const membership = new CallMembership(makeMockEvent(1000), membershipTemplate);
+            expect(membership.getAbsoluteExpiry()).toEqual(5000 + 1000);
+        });
 
-    it("rejects membership with no call_id", () => {
-        expect(() => {
-            new CallMembership(makeMockEvent(), Object.assign({}, membershipTemplate, { call_id: undefined }));
-        }).toThrow();
-    });
+        it("computes absolute expiry time based on expires_ts", () => {
+            const membership = new CallMembership(
+                makeMockEvent(1000),
+                Object.assign({}, membershipTemplate, { expires_ts: 6000 }),
+            );
+            expect(membership.getAbsoluteExpiry()).toEqual(5000 + 1000);
+        });
 
-    it("rejects membership with no scope", () => {
-        expect(() => {
-            new CallMembership(makeMockEvent(), Object.assign({}, membershipTemplate, { scope: undefined }));
-        }).toThrow();
-    });
-    it("rejects with malformatted expires_ts", () => {
-        expect(() => {
-            new CallMembership(makeMockEvent(), Object.assign({}, membershipTemplate, { expires_ts: "string" }));
-        }).toThrow();
-    });
-    it("rejects with malformatted expires", () => {
-        expect(() => {
-            new CallMembership(makeMockEvent(), Object.assign({}, membershipTemplate, { expires: "string" }));
-        }).toThrow();
-    });
+        it("considers memberships unexpired if local age low enough", () => {
+            const fakeEvent = makeMockEvent(1000);
+            fakeEvent.getLocalAge = jest.fn().mockReturnValue(3000);
+            const membership = new CallMembership(fakeEvent, membershipTemplate);
+            expect(membership.isExpired()).toEqual(false);
+        });
 
-    it("uses event timestamp if no created_ts", () => {
-        const membership = new CallMembership(makeMockEvent(12345), membershipTemplate);
-        expect(membership.createdTs()).toEqual(12345);
-    });
+        it("considers memberships expired when local age large", () => {
+            const fakeEvent = makeMockEvent(1000);
+            fakeEvent.localTimestamp = Date.now() - 6000;
+            const membership = new CallMembership(fakeEvent, membershipTemplate);
+            expect(membership.isExpired()).toEqual(true);
+        });
 
-    it("uses created_ts if present", () => {
-        const membership = new CallMembership(
-            makeMockEvent(12345),
-            Object.assign({}, membershipTemplate, { created_ts: 67890 }),
-        );
-        expect(membership.createdTs()).toEqual(67890);
+        it("returns preferred foci", () => {
+            const fakeEvent = makeMockEvent();
+            const mockFocus = { type: "this_is_a_mock_focus" };
+            const membership = new CallMembership(
+                fakeEvent,
+                Object.assign({}, membershipTemplate, { foci_active: [mockFocus] }),
+            );
+            expect(membership.getPreferredFoci()).toEqual([mockFocus]);
+        });
     });
 
-    it("computes absolute expiry time based on expires", () => {
-        const membership = new CallMembership(makeMockEvent(1000), membershipTemplate);
-        expect(membership.getAbsoluteExpiry()).toEqual(5000 + 1000);
-    });
+    describe("SessionMembershipData", () => {
+        const membershipTemplate: SessionMembershipData = {
+            call_id: "",
+            scope: "m.room",
+            application: "m.call",
+            device_id: "AAAAAAA",
+            focus_active: { type: "livekit" },
+            foci_preferred: [{ type: "livekit" }],
+        };
+
+        it("rejects membership with no device_id", () => {
+            expect(() => {
+                new CallMembership(makeMockEvent(), Object.assign({}, membershipTemplate, { device_id: undefined }));
+            }).toThrow();
+        });
 
-    it("computes absolute expiry time based on expires_ts", () => {
-        const membership = new CallMembership(
-            makeMockEvent(1000),
-            Object.assign({}, membershipTemplate, { expires: undefined, expires_ts: 6000 }),
-        );
-        expect(membership.getAbsoluteExpiry()).toEqual(5000 + 1000);
-    });
+        it("rejects membership with no call_id", () => {
+            expect(() => {
+                new CallMembership(makeMockEvent(), Object.assign({}, membershipTemplate, { call_id: undefined }));
+            }).toThrow();
+        });
 
-    it("considers memberships unexpired if local age low enough", () => {
-        const fakeEvent = makeMockEvent(1000);
-        fakeEvent.getLocalAge = jest.fn().mockReturnValue(3000);
-        const membership = new CallMembership(fakeEvent, membershipTemplate);
-        expect(membership.isExpired()).toEqual(false);
-    });
+        it("allow membership with no scope", () => {
+            expect(() => {
+                new CallMembership(makeMockEvent(), Object.assign({}, membershipTemplate, { scope: undefined }));
+            }).not.toThrow();
+        });
 
-    it("considers memberships expired when local age large", () => {
-        const fakeEvent = makeMockEvent(1000);
-        fakeEvent.localTimestamp = Date.now() - 6000;
-        const membership = new CallMembership(fakeEvent, membershipTemplate);
-        expect(membership.isExpired()).toEqual(true);
-    });
+        it("uses event timestamp if no created_ts", () => {
+            const membership = new CallMembership(makeMockEvent(12345), membershipTemplate);
+            expect(membership.createdTs()).toEqual(12345);
+        });
+
+        it("uses created_ts if present", () => {
+            const membership = new CallMembership(
+                makeMockEvent(12345),
+                Object.assign({}, membershipTemplate, { created_ts: 67890 }),
+            );
+            expect(membership.createdTs()).toEqual(67890);
+        });
+
+        it("considers memberships unexpired if local age low enough", () => {
+            const fakeEvent = makeMockEvent(1000);
+            fakeEvent.getLocalAge = jest.fn().mockReturnValue(3000);
+            const membership = new CallMembership(fakeEvent, membershipTemplate);
+            expect(membership.isExpired()).toEqual(false);
+        });
 
-    it("returns active foci", () => {
-        const fakeEvent = makeMockEvent();
-        const mockFocus = { type: "this_is_a_mock_focus" };
-        const membership = new CallMembership(
-            fakeEvent,
-            Object.assign({}, membershipTemplate, { foci_active: [mockFocus] }),
-        );
-        expect(membership.getActiveFoci()).toEqual([mockFocus]);
+        it("returns preferred foci", () => {
+            const fakeEvent = makeMockEvent();
+            const mockFocus = { type: "this_is_a_mock_focus" };
+            const membership = new CallMembership(
+                fakeEvent,
+                Object.assign({}, membershipTemplate, { foci_preferred: [mockFocus] }),
+            );
+            expect(membership.getPreferredFoci()).toEqual([mockFocus]);
+        });
     });
 
     describe("expiry calculation", () => {
         let fakeEvent: MatrixEvent;
         let membership: CallMembership;
+        const membershipTemplate: CallMembershipDataLegacy = {
+            call_id: "",
+            scope: "m.room",
+            application: "m.call",
+            device_id: "AAAAAAA",
+            expires: 5000,
+            membershipID: "bloop",
+            foci_active: [{ type: "livekit" }],
+        };
 
         beforeEach(() => {
             // server origin timestamp for this event is 1000
diff --git a/spec/unit/matrixrtc/LivekitFocus.spec.ts b/spec/unit/matrixrtc/LivekitFocus.spec.ts
new file mode 100644
index 00000000000..728d6a68de6
--- /dev/null
+++ b/spec/unit/matrixrtc/LivekitFocus.spec.ts
@@ -0,0 +1,60 @@
+/*
+Copyright 2023 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 { isLivekitFocus, isLivekitFocusActive, isLivekitFocusConfig } from "../../../src/matrixrtc/LivekitFocus";
+
+describe("LivekitFocus", () => {
+    it("isLivekitFocus", () => {
+        expect(
+            isLivekitFocus({
+                type: "livekit",
+                livekit_service_url: "http://test.com",
+                livekit_alias: "test",
+            }),
+        ).toBeTruthy();
+        expect(isLivekitFocus({ type: "livekit" })).toBeFalsy();
+        expect(
+            isLivekitFocus({ type: "not-livekit", livekit_service_url: "http://test.com", livekit_alias: "test" }),
+        ).toBeFalsy();
+        expect(
+            isLivekitFocus({ type: "livekit", other_service_url: "http://test.com", livekit_alias: "test" }),
+        ).toBeFalsy();
+        expect(
+            isLivekitFocus({ type: "livekit", livekit_service_url: "http://test.com", other_alias: "test" }),
+        ).toBeFalsy();
+    });
+    it("isLivekitFocusActive", () => {
+        expect(
+            isLivekitFocusActive({
+                type: "livekit",
+                focus_selection: "oldest_membership",
+            }),
+        ).toBeTruthy();
+        expect(isLivekitFocusActive({ type: "livekit" })).toBeFalsy();
+        expect(isLivekitFocusActive({ type: "not-livekit", focus_selection: "oldest_membership" })).toBeFalsy();
+    });
+    it("isLivekitFocusConfig", () => {
+        expect(
+            isLivekitFocusConfig({
+                type: "livekit",
+                livekit_service_url: "http://test.com",
+            }),
+        ).toBeTruthy();
+        expect(isLivekitFocusConfig({ type: "livekit" })).toBeFalsy();
+        expect(isLivekitFocusConfig({ type: "not-livekit", livekit_service_url: "http://test.com" })).toBeFalsy();
+        expect(isLivekitFocusConfig({ type: "livekit", other_service_url: "oldest_membership" })).toBeFalsy();
+    });
+});
diff --git a/spec/unit/matrixrtc/MatrixRTCSession.spec.ts b/spec/unit/matrixrtc/MatrixRTCSession.spec.ts
index b994613b5bb..e481be966d3 100644
--- a/spec/unit/matrixrtc/MatrixRTCSession.spec.ts
+++ b/spec/unit/matrixrtc/MatrixRTCSession.spec.ts
@@ -29,6 +29,7 @@ const membershipTemplate: CallMembershipData = {
     device_id: "AAAAAAA",
     expires: 60 * 60 * 1000,
     membershipID: "bloop",
+    foci_active: [{ type: "livekit", livekit_service_url: "https://lk.url" }],
 };
 
 const mockFocus = { type: "mock" };
@@ -198,6 +199,64 @@ describe("MatrixRTCSession", () => {
         });
     });
 
+    describe("getsActiveFocus", () => {
+        const activeFociConfig = { type: "livekit", livekit_service_url: "https://active.url" };
+        it("gets the correct active focus with oldest_membership", () => {
+            const mockRoom = makeMockRoom([
+                Object.assign({}, membershipTemplate, {
+                    device_id: "foo",
+                    created_ts: 500,
+                    foci_active: [activeFociConfig],
+                }),
+                Object.assign({}, membershipTemplate, { device_id: "old", created_ts: 1000 }),
+                Object.assign({}, membershipTemplate, { device_id: "bar", created_ts: 2000 }),
+            ]);
+
+            sess = MatrixRTCSession.roomSessionForRoom(client, mockRoom);
+
+            sess.joinRoomSession([{ type: "livekit", livekit_service_url: "htts://test.org" }], {
+                type: "livekit",
+                focus_selection: "oldest_membership",
+            });
+            expect(sess.getActiveFocus()).toBe(activeFociConfig);
+        });
+        it("does not provide focus if the selction method is unknown", () => {
+            const mockRoom = makeMockRoom([
+                Object.assign({}, membershipTemplate, {
+                    device_id: "foo",
+                    created_ts: 500,
+                    foci_active: [activeFociConfig],
+                }),
+                Object.assign({}, membershipTemplate, { device_id: "old", created_ts: 1000 }),
+                Object.assign({}, membershipTemplate, { device_id: "bar", created_ts: 2000 }),
+            ]);
+
+            sess = MatrixRTCSession.roomSessionForRoom(client, mockRoom);
+
+            sess.joinRoomSession([{ type: "livekit", livekit_service_url: "htts://test.org" }], {
+                type: "livekit",
+                focus_selection: "unknown",
+            });
+            expect(sess.getActiveFocus()).toBe(undefined);
+        });
+        it("gets the correct active focus legacy", () => {
+            const mockRoom = makeMockRoom([
+                Object.assign({}, membershipTemplate, {
+                    device_id: "foo",
+                    created_ts: 500,
+                    foci_active: [activeFociConfig],
+                }),
+                Object.assign({}, membershipTemplate, { device_id: "old", created_ts: 1000 }),
+                Object.assign({}, membershipTemplate, { device_id: "bar", created_ts: 2000 }),
+            ]);
+
+            sess = MatrixRTCSession.roomSessionForRoom(client, mockRoom);
+
+            sess.joinRoomSession([{ type: "livekit", livekit_service_url: "htts://test.org" }]);
+            expect(sess.getActiveFocus()).toBe(activeFociConfig);
+        });
+    });
+
     describe("joining", () => {
         let mockRoom: Room;
         let sendStateEventMock: jest.Mock;
@@ -223,13 +282,13 @@ describe("MatrixRTCSession", () => {
         });
 
         it("shows joined once join is called", () => {
-            sess!.joinRoomSession([mockFocus]);
+            sess!.joinRoomSession([mockFocus], mockFocus);
             expect(sess!.isJoined()).toEqual(true);
         });
 
         it("sends a membership event when joining a call", () => {
             jest.useFakeTimers();
-            sess!.joinRoomSession([mockFocus]);
+            sess!.joinRoomSession([mockFocus], mockFocus);
             expect(client.sendStateEvent).toHaveBeenCalledWith(
                 mockRoom!.roomId,
                 EventType.GroupCallMemberPrefix,
@@ -242,7 +301,8 @@ describe("MatrixRTCSession", () => {
                             device_id: "AAAAAAA",
                             expires: 3600000,
                             expires_ts: Date.now() + 3600000,
-                            foci_active: [{ type: "mock" }],
+                            foci_active: [mockFocus],
+
                             membershipID: expect.stringMatching(".*"),
                         },
                     ],
@@ -253,11 +313,11 @@ describe("MatrixRTCSession", () => {
         });
 
         it("does nothing if join called when already joined", () => {
-            sess!.joinRoomSession([mockFocus]);
+            sess!.joinRoomSession([mockFocus], mockFocus);
 
             expect(client.sendStateEvent).toHaveBeenCalledTimes(1);
 
-            sess!.joinRoomSession([mockFocus]);
+            sess!.joinRoomSession([mockFocus], mockFocus);
             expect(client.sendStateEvent).toHaveBeenCalledTimes(1);
         });
 
@@ -274,7 +334,7 @@ describe("MatrixRTCSession", () => {
                 const sendStateEventMock = jest.fn().mockImplementation(resolveFn);
                 client.sendStateEvent = sendStateEventMock;
 
-                sess!.joinRoomSession([mockFocus]);
+                sess!.joinRoomSession([mockFocus], mockFocus);
 
                 const eventContent = await eventSentPromise;
 
@@ -308,7 +368,7 @@ describe("MatrixRTCSession", () => {
                                 device_id: "AAAAAAA",
                                 expires: 3600000 * 2,
                                 expires_ts: 1000 + 3600000 * 2,
-                                foci_active: [{ type: "mock" }],
+                                foci_active: [mockFocus],
                                 created_ts: 1000,
                                 membershipID: expect.stringMatching(".*"),
                             },
@@ -322,7 +382,7 @@ describe("MatrixRTCSession", () => {
         });
 
         it("creates a key when joining", () => {
-            sess!.joinRoomSession([mockFocus], true);
+            sess!.joinRoomSession([mockFocus], mockFocus, { manageMediaKeys: true });
             const keys = sess?.getKeysForParticipant("@alice:example.org", "AAAAAAA");
             expect(keys).toHaveLength(1);
 
@@ -336,7 +396,7 @@ describe("MatrixRTCSession", () => {
                 sendEventMock.mockImplementation(resolve);
             });
 
-            sess!.joinRoomSession([mockFocus], true);
+            sess!.joinRoomSession([mockFocus], mockFocus, { manageMediaKeys: true });
 
             await eventSentPromise;
 
@@ -372,7 +432,7 @@ describe("MatrixRTCSession", () => {
                     });
                 });
 
-                sess!.joinRoomSession([mockFocus], true);
+                sess!.joinRoomSession([mockFocus], mockFocus, { manageMediaKeys: true });
                 jest.advanceTimersByTime(10000);
 
                 await eventSentPromise;
@@ -394,7 +454,7 @@ describe("MatrixRTCSession", () => {
                 throw e;
             });
 
-            sess!.joinRoomSession([mockFocus], true);
+            sess!.joinRoomSession([mockFocus], mockFocus, { manageMediaKeys: true });
 
             expect(client.cancelPendingEvent).toHaveBeenCalledWith(eventSentinel);
         });
@@ -409,7 +469,7 @@ describe("MatrixRTCSession", () => {
                     sendEventMock.mockImplementation(resolve);
                 });
 
-                sess.joinRoomSession([mockFocus], true);
+                sess.joinRoomSession([mockFocus], mockFocus, { manageMediaKeys: true });
                 await keysSentPromise1;
 
                 sendEventMock.mockClear();
@@ -462,7 +522,7 @@ describe("MatrixRTCSession", () => {
                     sendEventMock.mockImplementation((_roomId, _evType, payload) => resolve(payload));
                 });
 
-                sess.joinRoomSession([mockFocus], true);
+                sess.joinRoomSession([mockFocus], mockFocus, { manageMediaKeys: true });
                 const firstKeysPayload = await keysSentPromise1;
                 expect(firstKeysPayload.keys).toHaveLength(1);
 
@@ -499,7 +559,7 @@ describe("MatrixRTCSession", () => {
                     sendEventMock.mockImplementation(resolve);
                 });
 
-                sess.joinRoomSession([mockFocus], true);
+                sess.joinRoomSession([mockFocus], mockFocus, { manageMediaKeys: true });
                 await keysSentPromise1;
 
                 sendEventMock.mockClear();
@@ -595,7 +655,7 @@ describe("MatrixRTCSession", () => {
 
             jest.advanceTimersByTime(10000);
 
-            sess.joinRoomSession([mockFocus]);
+            sess.joinRoomSession([mockFocus], mockFocus);
 
             expect(client.sendStateEvent).toHaveBeenCalledWith(
                 mockRoomNoExpired!.roomId,
@@ -631,7 +691,7 @@ describe("MatrixRTCSession", () => {
         ]);
         sess = MatrixRTCSession.roomSessionForRoom(client, mockRoom);
 
-        sess.joinRoomSession([mockFocus]);
+        sess.joinRoomSession([mockFocus], mockFocus);
 
         expect(client.sendStateEvent).toHaveBeenCalledWith(
             mockRoom!.roomId,
@@ -645,6 +705,7 @@ describe("MatrixRTCSession", () => {
                         device_id: "OTHERDEVICE",
                         expires: 3600000,
                         created_ts: 1000,
+                        foci_active: [{ type: "livekit", livekit_service_url: "https://lk.url" }],
                         membershipID: expect.stringMatching(".*"),
                     },
                     {
diff --git a/spec/unit/matrixrtc/MatrixRTCSessionManager.spec.ts b/spec/unit/matrixrtc/MatrixRTCSessionManager.spec.ts
index f5ffc13e05b..c2e6fc52f45 100644
--- a/spec/unit/matrixrtc/MatrixRTCSessionManager.spec.ts
+++ b/spec/unit/matrixrtc/MatrixRTCSessionManager.spec.ts
@@ -35,6 +35,7 @@ const membershipTemplate: CallMembershipData = {
     device_id: "AAAAAAA",
     expires: 60 * 60 * 1000,
     membershipID: "bloop",
+    foci_active: [{ type: "test" }],
 };
 
 describe("MatrixRTCSessionManager", () => {
diff --git a/src/@types/event.ts b/src/@types/event.ts
index 44ef4c1434c..c01fc40d3e8 100644
--- a/src/@types/event.ts
+++ b/src/@types/event.ts
@@ -57,6 +57,7 @@ import {
 } from "../webrtc/callEventTypes";
 import { EncryptionKeysEventContent, ICallNotifyContent } from "../matrixrtc/types";
 import { M_POLL_END, M_POLL_START, PollEndEventContent, PollStartEventContent } from "./polls";
+import { SessionMembershipData } from "../matrixrtc/CallMembership";
 
 export enum EventType {
     // Room state events
@@ -356,7 +357,10 @@ export interface StateEvents {
 
     // MSC3401
     [EventType.GroupCallPrefix]: IGroupCallRoomState;
-    [EventType.GroupCallMemberPrefix]: XOR<IGroupCallRoomMemberState, ExperimentalGroupCallRoomMemberState>;
+    [EventType.GroupCallMemberPrefix]: XOR<
+        XOR<IGroupCallRoomMemberState, ExperimentalGroupCallRoomMemberState>,
+        XOR<SessionMembershipData, {}>
+    >;
 
     // MSC3089
     [UNSTABLE_MSC3089_BRANCH.name]: MSC3089EventContent;
diff --git a/src/matrixrtc/CallMembership.ts b/src/matrixrtc/CallMembership.ts
index 171751f1d1f..52893841d89 100644
--- a/src/matrixrtc/CallMembership.ts
+++ b/src/matrixrtc/CallMembership.ts
@@ -14,52 +14,114 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+import { EitherAnd } from "matrix-events-sdk/lib/types";
+
 import { MatrixEvent } from "../matrix";
 import { deepCompare } from "../utils";
 import { Focus } from "./focus";
+import { isLivekitFocusActive } from "./LivekitFocus";
 
 type CallScope = "m.room" | "m.user";
-
 // Represents an entry in the memberships section of an m.call.member event as it is on the wire
-export interface CallMembershipData {
-    application?: string;
+
+// There are two different data interfaces. One for the Legacy types and one compliant with MSC4143
+
+// MSC4143 (MatrixRTC) session membership data
+
+export type SessionMembershipData = {
+    application: string;
+    call_id: string;
+    device_id: string;
+
+    focus_active: Focus;
+    foci_preferred: Focus[];
+    created_ts?: number;
+
+    // Application specific data
+    scope?: CallScope;
+};
+
+export const isSessionMembershipData = (data: CallMembershipData): data is SessionMembershipData =>
+    "focus_active" in data;
+
+const checkSessionsMembershipData = (data: any, errors: string[]): data is SessionMembershipData => {
+    const prefix = "Malformed session membership event: ";
+    if (typeof data.device_id !== "string") errors.push(prefix + "device_id must be string");
+    if (typeof data.call_id !== "string") errors.push(prefix + "call_id must be string");
+    if (typeof data.application !== "string") errors.push(prefix + "application must be a string");
+    if (typeof data.focus_active?.type !== "string") errors.push(prefix + "focus_active.type must be a string");
+    if (!Array.isArray(data.foci_preferred)) errors.push(prefix + "foci_preferred must be an array");
+    // optional parameters
+    if (data.created_ts && typeof data.created_ts !== "number") errors.push(prefix + "created_ts must be number");
+
+    // application specific data (we first need to check if they exist)
+    if (data.scope && typeof data.scope !== "string") errors.push(prefix + "scope must be string");
+    return errors.length === 0;
+};
+
+// Legacy session membership data
+
+export type CallMembershipDataLegacy = {
+    application: string;
     call_id: string;
     scope: CallScope;
     device_id: string;
+    membershipID: string;
     created_ts?: number;
-    expires?: number;
-    expires_ts?: number;
     foci_active?: Focus[];
-    membershipID: string;
-}
+} & EitherAnd<{ expires: number }, { expires_ts: number }>;
+
+export const isLegacyCallMembershipData = (data: CallMembershipData): data is CallMembershipDataLegacy =>
+    "membershipID" in data;
+
+const checkCallMembershipDataLegacy = (data: any, errors: string[]): data is CallMembershipDataLegacy => {
+    const prefix = "Malformed legacy rtc membership event: ";
+    if (!("expires" in data || "expires_ts" in data)) {
+        errors.push(prefix + "expires_ts or expires must be present");
+    }
+    if ("expires" in data) {
+        if (typeof data.expires !== "number") {
+            errors.push(prefix + "expires must be numeric");
+        }
+    }
+    if ("expires_ts" in data) {
+        if (typeof data.expires_ts !== "number") {
+            errors.push(prefix + "expires_ts must be numeric");
+        }
+    }
+
+    if (typeof data.device_id !== "string") errors.push(prefix + "device_id must be string");
+    if (typeof data.call_id !== "string") errors.push(prefix + "call_id must be string");
+    if (typeof data.application !== "string") errors.push(prefix + "application must be a string");
+    if (typeof data.membershipID !== "string") errors.push(prefix + "membershipID must be a string");
+    // optional elements
+    if (data.created_ts && typeof data.created_ts !== "number") errors.push(prefix + "created_ts must be number");
+    // application specific data (we first need to check if they exist)
+    if (data.scope && typeof data.scope !== "string") errors.push(prefix + "scope must be string");
+    return errors.length === 0;
+};
+
+export type CallMembershipData = CallMembershipDataLegacy | SessionMembershipData;
 
 export class CallMembership {
     public static equal(a: CallMembership, b: CallMembership): boolean {
-        return deepCompare(a.data, b.data);
+        return deepCompare(a.membershipData, b.membershipData);
     }
+    private membershipData: CallMembershipData;
 
     public constructor(
         private parentEvent: MatrixEvent,
-        private data: CallMembershipData,
+        data: any,
     ) {
-        if (!(data.expires || data.expires_ts)) {
-            throw new Error("Malformed membership: expires_ts or expires must be present");
-        }
-        if (data.expires) {
-            if (typeof data.expires !== "number") {
-                throw new Error("Malformed membership: expires must be numeric");
-            }
-        }
-        if (data.expires_ts) {
-            if (typeof data.expires_ts !== "number") {
-                throw new Error("Malformed membership: expires_ts must be numeric");
-            }
+        const sessionErrors: string[] = [];
+        const legacyErrors: string[] = [];
+        if (!checkSessionsMembershipData(data, sessionErrors) && !checkCallMembershipDataLegacy(data, legacyErrors)) {
+            throw Error(
+                `unknown CallMembership data. Does not match legacy call.member (${legacyErrors.join(" & ")}) events nor MSC4143 (${sessionErrors.join(" & ")})`,
+            );
+        } else {
+            this.membershipData = data;
         }
-
-        if (typeof data.device_id !== "string") throw new Error("Malformed membership event: device_id must be string");
-        if (typeof data.call_id !== "string") throw new Error("Malformed membership event: call_id must be string");
-        if (typeof data.scope !== "string") throw new Error("Malformed membership event: scope must be string");
-        if (!parentEvent.getSender()) throw new Error("Invalid parent event: sender is null");
     }
 
     public get sender(): string | undefined {
@@ -67,62 +129,89 @@ export class CallMembership {
     }
 
     public get callId(): string {
-        return this.data.call_id;
+        return this.membershipData.call_id;
     }
 
     public get deviceId(): string {
-        return this.data.device_id;
+        return this.membershipData.device_id;
     }
 
     public get application(): string | undefined {
-        return this.data.application;
+        return this.membershipData.application;
     }
 
-    public get scope(): CallScope {
-        return this.data.scope;
+    public get scope(): CallScope | undefined {
+        return this.membershipData.scope;
     }
 
     public get membershipID(): string {
-        return this.data.membershipID;
+        if (isLegacyCallMembershipData(this.membershipData)) return this.membershipData.membershipID;
+        // the createdTs behaves equivalent to the membershipID.
+        // we only need the field for the legacy member envents where we needed to update them
+        // synapse ignores sending state events if they have the same content.
+        else return this.createdTs().toString();
     }
 
     public createdTs(): number {
-        return this.data.created_ts ?? this.parentEvent.getTs();
+        return this.membershipData.created_ts ?? this.parentEvent.getTs();
     }
 
-    public getAbsoluteExpiry(): number {
-        if (this.data.expires) {
-            return this.createdTs() + this.data.expires;
+    public getAbsoluteExpiry(): number | undefined {
+        if (!isLegacyCallMembershipData(this.membershipData)) return undefined;
+        if ("expires" in this.membershipData) {
+            // we know createdTs exists since we already do the isLegacyCallMembershipData check
+            return this.createdTs() + this.membershipData.expires;
         } else {
             // We know it exists because we checked for this in the constructor.
-            return this.data.expires_ts!;
+            return this.membershipData.expires_ts;
         }
     }
 
     // gets the expiry time of the event, converted into the device's local time
-    public getLocalExpiry(): number {
-        if (this.data.expires) {
+    public getLocalExpiry(): number | undefined {
+        if (!isLegacyCallMembershipData(this.membershipData)) return undefined;
+        if ("expires" in this.membershipData) {
+            // we know createdTs exists since we already do the isLegacyCallMembershipData check
             const relativeCreationTime = this.parentEvent.getTs() - this.createdTs();
 
             const localCreationTs = this.parentEvent.localTimestamp - relativeCreationTime;
 
-            return localCreationTs + this.data.expires;
+            return localCreationTs + this.membershipData.expires;
         } else {
             // With expires_ts we cannot convert to local time.
             // TODO: Check the server timestamp and compute a diff to local time.
-            return this.data.expires_ts!;
+            return this.membershipData.expires_ts;
         }
     }
 
-    public getMsUntilExpiry(): number {
-        return this.getLocalExpiry() - Date.now();
+    public getMsUntilExpiry(): number | undefined {
+        if (isLegacyCallMembershipData(this.membershipData)) return this.getLocalExpiry()! - Date.now();
     }
 
     public isExpired(): boolean {
-        return this.getMsUntilExpiry() <= 0;
+        if (isLegacyCallMembershipData(this.membershipData)) return this.getMsUntilExpiry()! <= 0;
+
+        // MSC4143 events expire by being updated. So if the event exists, its not expired.
+        return false;
+    }
+
+    public getPreferredFoci(): Focus[] {
+        // To support both, the new and the old MatrixRTC memberships have two cases based
+        // on the availablitiy of `foci_preferred`
+        if (isLegacyCallMembershipData(this.membershipData)) return this.membershipData.foci_active ?? [];
+
+        // MSC4143 style membership
+        return this.membershipData.foci_preferred;
     }
 
-    public getActiveFoci(): Focus[] {
-        return this.data.foci_active ?? [];
+    public getFocusSelection(): string | undefined {
+        if (isLegacyCallMembershipData(this.membershipData)) {
+            return "oldest_membership";
+        } else {
+            const focusActive = this.membershipData.focus_active;
+            if (isLivekitFocusActive(focusActive)) {
+                return focusActive.focus_selection;
+            }
+        }
     }
 }
diff --git a/src/matrixrtc/LivekitFocus.ts b/src/matrixrtc/LivekitFocus.ts
new file mode 100644
index 00000000000..0a42dda5fd5
--- /dev/null
+++ b/src/matrixrtc/LivekitFocus.ts
@@ -0,0 +1,39 @@
+/*
+Copyright 2023 New Vector Ltd
+
+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 { Focus } from "./focus";
+
+export interface LivekitFocusConfig extends Focus {
+    type: "livekit";
+    livekit_service_url: string;
+}
+
+export const isLivekitFocusConfig = (object: any): object is LivekitFocusConfig =>
+    object.type === "livekit" && "livekit_service_url" in object;
+
+export interface LivekitFocus extends LivekitFocusConfig {
+    livekit_alias: string;
+}
+
+export const isLivekitFocus = (object: any): object is LivekitFocus =>
+    isLivekitFocusConfig(object) && "livekit_alias" in object;
+
+export interface LivekitFocusActive extends Focus {
+    type: "livekit";
+    focus_selection: "oldest_membership";
+}
+export const isLivekitFocusActive = (object: any): object is LivekitFocusActive =>
+    object.type === "livekit" && "focus_selection" in object;
diff --git a/src/matrixrtc/MatrixRTCSession.ts b/src/matrixrtc/MatrixRTCSession.ts
index 7421723ecb4..e7fbd7a48bf 100644
--- a/src/matrixrtc/MatrixRTCSession.ts
+++ b/src/matrixrtc/MatrixRTCSession.ts
@@ -20,7 +20,13 @@ import { EventTimeline } from "../models/event-timeline";
 import { Room } from "../models/room";
 import { MatrixClient } from "../client";
 import { EventType } from "../@types/event";
-import { CallMembership, CallMembershipData } from "./CallMembership";
+import {
+    CallMembership,
+    CallMembershipData,
+    CallMembershipDataLegacy,
+    SessionMembershipData,
+    isLegacyCallMembershipData,
+} from "./CallMembership";
 import { RoomStateEvent } from "../models/room-state";
 import { Focus } from "./focus";
 import { randomString, secureRandomBase64Url } from "../randomstring";
@@ -29,6 +35,8 @@ import { decodeBase64, encodeUnpaddedBase64 } from "../base64";
 import { KnownMembership } from "../@types/membership";
 import { MatrixError } from "../http-api/errors";
 import { MatrixEvent } from "../models/event";
+import { isLivekitFocusActive } from "./LivekitFocus";
+import { ExperimentalGroupCallRoomMemberState } from "../webrtc/groupCall";
 
 const MEMBERSHIP_EXPIRY_TIME = 60 * 60 * 1000;
 const MEMBER_EVENT_CHECK_PERIOD = 2 * 60 * 1000; // How often we check to see if we need to re-send our member event
@@ -57,7 +65,7 @@ export enum MatrixRTCSessionEvent {
     MembershipsChanged = "memberships_changed",
     // We joined or left the session: our own local idea of whether we are joined,
     // separate from MembershipsChanged, ie. independent of whether our member event
-    // has succesfully gone through.
+    // has successfully gone through.
     JoinStateChanged = "join_state_changed",
     // The key used to encrypt media has changed
     EncryptionKeyChanged = "encryption_key_changed",
@@ -75,7 +83,20 @@ export type MatrixRTCSessionEventHandlerMap = {
         participantId: string,
     ) => void;
 };
-
+export interface JoinSessionConfig {
+    /** If true, generate and share a media key for this participant,
+     *  and emit MatrixRTCSessionEvent.EncryptionKeyChanged when
+     *  media keys for other participants become available.
+     */
+    manageMediaKeys?: boolean;
+    /** Lets you configure how the events for the session are formatted.
+     *   - legacy: use one event with a membership array.
+     *   - MSC4143: use one event per membership (with only one membership per event)
+     * More details can be found in MSC4143 and by checking the types:
+     * `CallMembershipDataLegacy` and `SessionMembershipData`
+     */
+    useLegacyMemberEvents?: boolean;
+}
 /**
  * A MatrixRTCSession manages the membership & properties of a MatrixRTC session.
  * This class doesn't deal with media at all, just membership & properties of a session.
@@ -102,12 +123,16 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
     private makeNewKeyTimeout?: ReturnType<typeof setTimeout>;
     private setNewKeyTimeouts = new Set<ReturnType<typeof setTimeout>>();
 
-    private activeFoci: Focus[] | undefined;
+    // This is a Focus with the specified fields for an ActiveFocus (e.g. LivekitFocusActive for type="livekit")
+    private ownFocusActive?: Focus;
+    // This is a Foci array that contains the Focus objects this user is aware of and proposes to use.
+    private ownFociPreferred?: Focus[];
 
     private updateCallMembershipRunning = false;
     private needCallMembershipUpdate = false;
 
     private manageMediaKeys = false;
+    private useLegacyMemberEvents = true;
     // userId:deviceId => array of keys
     private encryptionKeys = new Map<string, Array<Uint8Array>>();
     private lastEncryptionKeyUpdateRequest?: number;
@@ -134,21 +159,33 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
 
         const callMemberships: CallMembership[] = [];
         for (const memberEvent of callMemberEvents) {
-            const eventMemberships: CallMembershipData[] = memberEvent.getContent()["memberships"];
-            if (eventMemberships === undefined) {
-                continue;
+            const content = memberEvent.getContent();
+            let membershipContents: any[] = [];
+            // We first decide if its a MSC4143 event (per device state key)
+            if ("memberships" in content) {
+                // we have a legacy (one event for all devices) event
+                if (!Array.isArray(content["memberships"])) {
+                    logger.warn(`Malformed member event from ${memberEvent.getSender()}: memberships is not an array`);
+                    continue;
+                }
+                membershipContents = content["memberships"];
+            } else {
+                // We have a MSC4143 event membership event
+                if (Object.keys(content).length !== 0) {
+                    // We checked for empty content to not try to construct CallMembership's with {}.
+                    membershipContents.push(content);
+                }
             }
-            if (!Array.isArray(eventMemberships)) {
-                logger.warn(`Malformed member event from ${memberEvent.getSender()}: memberships is not an array`);
+            if (membershipContents.length === 0) {
                 continue;
             }
 
-            for (const membershipData of eventMemberships) {
+            for (const membershipData of membershipContents) {
                 try {
                     const membership = new CallMembership(memberEvent, membershipData);
 
                     if (membership.callId !== "" || membership.scope !== "m.room") {
-                        // for now, just ignore anything that isn't the a room scope call
+                        // for now, just ignore anything that isn't a room scope call
                         logger.info(`Ignoring user-scoped call`);
                         continue;
                     }
@@ -202,6 +239,7 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
 
     /*
      * Returns true if we intend to be participating in the MatrixRTC session.
+     * This is determined by checking if the relativeExpiry has been set.
      */
     public isJoined(): boolean {
         return this.relativeExpiry !== undefined;
@@ -232,30 +270,34 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
      * desired.
      * This method will return immediately and the session will be joined in the background.
      *
-     * @param activeFoci - The list of foci to set as currently active in the call member event
-     * @param manageMediaKeys - If true, generate and share a a media key for this participant,
-     *                          and emit MatrixRTCSessionEvent.EncryptionKeyChanged when
-     *                          media keys for other participants become available.
+     * @param fociActive - The object representing the active focus. (This depends on the focus type.)
+     * @param fociPreferred - The list of preferred foci this member proposes to use/knows/has access to.
+     *                        For the livekit case this is a list of foci generated from the homeserver well-known, the current rtc session,
+     *                        or optionally other room members homeserver well known.
+     * @param joinConfig - Additional configuration for the joined session.
      */
-    public joinRoomSession(activeFoci: Focus[], manageMediaKeys?: boolean): void {
+    public joinRoomSession(fociPreferred: Focus[], fociActive?: Focus, joinConfig?: JoinSessionConfig): void {
         if (this.isJoined()) {
             logger.info(`Already joined to session in room ${this.room.roomId}: ignoring join call`);
             return;
         }
 
-        logger.info(`Joining call session in room ${this.room.roomId} with manageMediaKeys=${manageMediaKeys}`);
-        this.activeFoci = activeFoci;
+        this.ownFocusActive = fociActive;
+        this.ownFociPreferred = fociPreferred;
         this.relativeExpiry = MEMBERSHIP_EXPIRY_TIME;
-        this.manageMediaKeys = manageMediaKeys ?? false;
+        this.manageMediaKeys = joinConfig?.manageMediaKeys ?? this.manageMediaKeys;
+        this.useLegacyMemberEvents = joinConfig?.useLegacyMemberEvents ?? this.useLegacyMemberEvents;
         this.membershipId = randomString(5);
-        this.emit(MatrixRTCSessionEvent.JoinStateChanged, true);
-        if (manageMediaKeys) {
+
+        logger.info(`Joining call session in room ${this.room.roomId} with manageMediaKeys=${this.manageMediaKeys}`);
+        if (joinConfig?.manageMediaKeys) {
             this.makeNewSenderKey();
             this.requestKeyEventSend();
         }
         // We don't wait for this, mostly because it may fail and schedule a retry, so this
         // function returning doesn't really mean anything at all.
         this.triggerCallMembershipEventUpdate();
+        this.emit(MatrixRTCSessionEvent.JoinStateChanged, true);
     }
 
     /**
@@ -295,7 +337,7 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
 
         logger.info(`Leaving call session in room ${this.room.roomId}`);
         this.relativeExpiry = undefined;
-        this.activeFoci = undefined;
+        this.ownFocusActive = undefined;
         this.manageMediaKeys = false;
         this.membershipId = undefined;
         this.emit(MatrixRTCSessionEvent.JoinStateChanged, false);
@@ -315,6 +357,21 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
         });
     }
 
+    public getActiveFocus(): Focus | undefined {
+        if (this.ownFocusActive && isLivekitFocusActive(this.ownFocusActive)) {
+            // A livekit active focus
+            if (this.ownFocusActive.focus_selection === "oldest_membership") {
+                const oldestMembership = this.getOldestMembership();
+                return oldestMembership?.getPreferredFoci()[0];
+            }
+        }
+        if (!this.ownFocusActive) {
+            // we use the legacy call.member events so default to oldest member
+            const oldestMembership = this.getOldestMembership();
+            return oldestMembership?.getPreferredFoci()[0];
+        }
+    }
+
     public getKeysForParticipant(userId: string, deviceId: string): Array<Uint8Array> | undefined {
         return this.encryptionKeys.get(getParticipantId(userId, deviceId));
     }
@@ -344,7 +401,7 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
      * @param userId - The user ID of the participant
      * @param deviceId - Device ID of the participant
      * @param encryptionKeyIndex - The index of the key to set
-     * @param encryptionKeyString - The string represenation of the key to set in base64
+     * @param encryptionKeyString - The string representation of the key to set in base64
      * @param delayBeforeuse - If true, delay before emitting a key changed event. Useful when setting
      *                         encryption keys for the local participant to allow time for the key to
      *                         be distributed.
@@ -379,7 +436,7 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
 
     /**
      * Generate a new sender key and add it at the next available index
-     * @param delayBeforeUse - If true, wait for a short period before settign the key for the
+     * @param delayBeforeUse - If true, wait for a short period before setting the key for the
      *                         media encryptor to use. If false, set the key immediately.
      */
     private makeNewSenderKey(delayBeforeUse = false): void {
@@ -488,7 +545,9 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
         let soonestExpiry;
         for (const membership of this.memberships) {
             const thisExpiry = membership.getMsUntilExpiry();
-            if (soonestExpiry === undefined || thisExpiry < soonestExpiry) {
+            // If getMsUntilExpiry is undefined we have a MSC4143 (MatrixRTC) compliant event - it never expires
+            // but will be reliably resent on disconnect.
+            if (thisExpiry !== undefined && (soonestExpiry === undefined || thisExpiry < soonestExpiry)) {
                 soonestExpiry = thisExpiry;
             }
         }
@@ -502,6 +561,13 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
         return this.memberships[0];
     }
 
+    public getFocusInUse(): Focus | undefined {
+        const oldestMembership = this.getOldestMembership();
+        if (oldestMembership?.getFocusSelection() === "oldest_membership") {
+            return oldestMembership.getPreferredFoci()[0];
+        }
+    }
+
     public onCallEncryption = (event: MatrixEvent): void => {
         const userId = event.getSender();
         const content = event.getContent<EncryptionKeysEventContent>();
@@ -613,30 +679,41 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
      * Constructs our own membership
      * @param prevMembership - The previous value of our call membership, if any
      */
-    private makeMyMembership(prevMembership?: CallMembership): CallMembershipData {
+    private makeMyMembershipLegacy(deviceId: string, prevMembership?: CallMembership): CallMembershipDataLegacy {
         if (this.relativeExpiry === undefined) {
             throw new Error("Tried to create our own membership event when we're not joined!");
         }
         if (this.membershipId === undefined) {
             throw new Error("Tried to create our own membership event when we have no membership ID!");
         }
-
-        const m: CallMembershipData = {
+        const createdTs = prevMembership?.createdTs();
+        return {
             call_id: "",
             scope: "m.room",
             application: "m.call",
-            device_id: this.client.getDeviceId()!,
+            device_id: deviceId,
             expires: this.relativeExpiry,
-            foci_active: this.activeFoci,
+            // TODO: Date.now() should be the origin_server_ts (now).
+            expires_ts: this.relativeExpiry + (createdTs ?? Date.now()),
+            // we use the fociPreferred since this is the list of foci.
+            // it is named wrong in the Legacy events.
+            foci_active: this.ownFociPreferred,
             membershipID: this.membershipId,
+            ...(createdTs ? { created_ts: createdTs } : {}),
+        };
+    }
+    /**
+     * Constructs our own membership
+     */
+    private makeMyMembership(deviceId: string): SessionMembershipData {
+        return {
+            call_id: "",
+            scope: "m.room",
+            application: "m.call",
+            device_id: deviceId,
+            focus_active: { type: "livekit", focus_selection: "oldest_membership" },
+            foci_preferred: this.ownFociPreferred ?? [],
         };
-
-        if (prevMembership) m.created_ts = prevMembership.createdTs();
-        if (m.created_ts) m.expires_ts = m.created_ts + (m.expires ?? 0);
-        // TODO: Date.now() should be the origin_server_ts (now).
-        else m.expires_ts = Date.now() + (m.expires ?? 0);
-
-        return m;
     }
 
     /**
@@ -646,36 +723,41 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
         myPrevMembershipData?: CallMembershipData,
         myPrevMembership?: CallMembership,
     ): boolean {
-        // work out if we need to update our membership event
-        let needsUpdate = false;
+        if (myPrevMembership && myPrevMembership.getMsUntilExpiry() === undefined) return false;
+
         // Need to update if there's a membership for us but we're not joined (valid or otherwise)
-        if (!this.isJoined() && myPrevMembershipData) needsUpdate = true;
-        if (this.isJoined()) {
-            // ...or if we are joined, but there's no valid membership event
-            if (!myPrevMembership) {
-                needsUpdate = true;
-            } else if (myPrevMembership.getMsUntilExpiry() < MEMBERSHIP_EXPIRY_TIME / 2) {
-                // ...or if the expiry time needs bumping
-                needsUpdate = true;
-                this.relativeExpiry! += MEMBERSHIP_EXPIRY_TIME;
-            }
+        if (!this.isJoined()) return !!myPrevMembershipData;
+
+        // ...or if we are joined, but there's no valid membership event
+        if (!myPrevMembership) return true;
+
+        const expiryTime = myPrevMembership.getMsUntilExpiry();
+        if (expiryTime !== undefined && expiryTime < MEMBERSHIP_EXPIRY_TIME / 2) {
+            // ...or if the expiry time needs bumping
+            this.relativeExpiry! += MEMBERSHIP_EXPIRY_TIME;
+            return true;
         }
 
-        return needsUpdate;
+        return false;
     }
 
+    private makeNewMembership(deviceId: string): SessionMembershipData | {} {
+        // If we're joined, add our own
+        if (this.isJoined()) {
+            return this.makeMyMembership(deviceId);
+        }
+        return {};
+    }
     /**
      * Makes a new membership list given the old list alonng with this user's previous membership event
      * (if any) and this device's previous membership (if any)
      */
-    private makeNewMemberships(
+    private makeNewLegacyMemberships(
         oldMemberships: CallMembershipData[],
+        localDeviceId: string,
         myCallMemberEvent?: MatrixEvent,
         myPrevMembership?: CallMembership,
-    ): CallMembershipData[] {
-        const localDeviceId = this.client.getDeviceId();
-        if (!localDeviceId) throw new Error("Local device ID is null!");
-
+    ): ExperimentalGroupCallRoomMemberState {
         const filterExpired = (m: CallMembershipData): boolean => {
             let membershipObj;
             try {
@@ -704,10 +786,10 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
 
         // If we're joined, add our own
         if (this.isJoined()) {
-            newMemberships.push(this.makeMyMembership(myPrevMembership));
+            newMemberships.push(this.makeMyMembershipLegacy(localDeviceId, myPrevMembership));
         }
 
-        return newMemberships;
+        return { memberships: newMemberships };
     }
 
     private triggerCallMembershipEventUpdate = async (): Promise<void> => {
@@ -742,46 +824,54 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
         if (!localUserId || !localDeviceId) throw new Error("User ID or device ID was null!");
 
         const myCallMemberEvent = roomState.getStateEvents(EventType.GroupCallMemberPrefix, localUserId) ?? undefined;
-        const content = myCallMemberEvent?.getContent<Record<any, unknown>>() ?? {};
-        const memberships: CallMembershipData[] = Array.isArray(content["memberships"]) ? content["memberships"] : [];
-
-        const myPrevMembershipData = memberships.find((m) => m.device_id === localDeviceId);
-        let myPrevMembership;
-        try {
-            if (myCallMemberEvent && myPrevMembershipData && myPrevMembershipData.membershipID === this.membershipId) {
-                myPrevMembership = new CallMembership(myCallMemberEvent, myPrevMembershipData);
+        const content = myCallMemberEvent?.getContent() ?? {};
+        const legacy = "memberships" in content || this.useLegacyMemberEvents;
+        let newContent: {} | ExperimentalGroupCallRoomMemberState | SessionMembershipData = {};
+        if (legacy) {
+            let myPrevMembership: CallMembership | undefined;
+            // We know its CallMembershipDataLegacy
+            const memberships: CallMembershipDataLegacy[] = Array.isArray(content["memberships"])
+                ? content["memberships"]
+                : [];
+            const myPrevMembershipData = memberships.find((m) => m.device_id === localDeviceId);
+            try {
+                if (
+                    myCallMemberEvent &&
+                    myPrevMembershipData &&
+                    isLegacyCallMembershipData(myPrevMembershipData) &&
+                    myPrevMembershipData.membershipID === this.membershipId
+                ) {
+                    myPrevMembership = new CallMembership(myCallMemberEvent, myPrevMembershipData);
+                }
+            } catch (e) {
+                // This would indicate a bug or something weird if our own call membership
+                // wasn't valid
+                logger.warn("Our previous call membership was invalid - this shouldn't happen.", e);
             }
-        } catch (e) {
-            // This would indicate a bug or something weird if our own call membership
-            // wasn't valid
-            logger.warn("Our previous call membership was invalid - this shouldn't happen.", e);
-        }
-
-        if (myPrevMembership) {
-            logger.debug(`${myPrevMembership.getMsUntilExpiry()} until our membership expires`);
-        }
-
-        if (!this.membershipEventNeedsUpdate(myPrevMembershipData, myPrevMembership)) {
-            // nothing to do - reschedule the check again
-            this.memberEventTimeout = setTimeout(this.triggerCallMembershipEventUpdate, MEMBER_EVENT_CHECK_PERIOD);
-            return;
+            if (myPrevMembership) {
+                logger.debug(`${myPrevMembership.getMsUntilExpiry()} until our membership expires`);
+            }
+            if (!this.membershipEventNeedsUpdate(myPrevMembershipData, myPrevMembership)) {
+                // nothing to do - reschedule the check again
+                this.memberEventTimeout = setTimeout(this.triggerCallMembershipEventUpdate, MEMBER_EVENT_CHECK_PERIOD);
+                return;
+            }
+            newContent = this.makeNewLegacyMemberships(memberships, localDeviceId, myCallMemberEvent, myPrevMembership);
+        } else {
+            newContent = this.makeNewMembership(localDeviceId);
         }
 
-        const newContent = {
-            memberships: this.makeNewMemberships(memberships, myCallMemberEvent, myPrevMembership),
-        };
-
         try {
             await this.client.sendStateEvent(
                 this.room.roomId,
                 EventType.GroupCallMemberPrefix,
                 newContent,
-                localUserId,
+                this.useLegacyMemberEvents ? localUserId : `${localUserId}_${localDeviceId}`,
             );
             logger.info(`Sent updated call member event.`);
 
             // check periodically to see if we need to refresh our member event
-            if (this.isJoined()) {
+            if (this.isJoined() && legacy) {
                 this.memberEventTimeout = setTimeout(this.triggerCallMembershipEventUpdate, MEMBER_EVENT_CHECK_PERIOD);
             }
         } catch (e) {
diff --git a/src/matrixrtc/MatrixRTCSessionManager.ts b/src/matrixrtc/MatrixRTCSessionManager.ts
index 188f7b3e176..2fd5d2583f7 100644
--- a/src/matrixrtc/MatrixRTCSessionManager.ts
+++ b/src/matrixrtc/MatrixRTCSessionManager.ts
@@ -73,9 +73,9 @@ export class MatrixRTCSessionManager extends TypedEventEmitter<MatrixRTCSessionM
         }
         this.roomSessions.clear();
 
-        this.client.removeListener(ClientEvent.Room, this.onRoom);
-        this.client.removeListener(RoomEvent.Timeline, this.onTimeline);
-        this.client.removeListener(RoomStateEvent.Events, this.onRoomState);
+        this.client.off(ClientEvent.Room, this.onRoom);
+        this.client.off(RoomEvent.Timeline, this.onTimeline);
+        this.client.off(RoomStateEvent.Events, this.onRoomState);
     }
 
     /**
diff --git a/src/matrixrtc/focus.ts b/src/matrixrtc/focus.ts
index 6892bbf15c0..cf9836dd450 100644
--- a/src/matrixrtc/focus.ts
+++ b/src/matrixrtc/focus.ts
@@ -21,4 +21,5 @@ limitations under the License.
  */
 export interface Focus {
     type: string;
+    [key: string]: unknown;
 }