diff --git a/playwright/url-transport.spec.ts b/playwright/url-transport.spec.ts
index 994c0f5cc..6400657fe 100644
--- a/playwright/url-transport.spec.ts
+++ b/playwright/url-transport.spec.ts
@@ -8,6 +8,7 @@ Please see LICENSE in the repository root for full details.
 import { expect, type Page, test } from "@playwright/test";
 
 import { SpaHelpers } from "./spa-helpers";
+import { type RtcMode } from "./widget/test-helpers.ts";
 
 const sfuUrl = "wss://matrix-rtc.m.localhost/livekit/sfu";
 const serviceUrl = "https://matrix-rtc.m.localhost/livekit/jwt";
@@ -41,6 +42,8 @@ type Flow = "cs-api" | "service-legacy" | "service-default";
 const cases: {
   hostShape: Shape;
   guestShape: Shape;
+  /** The MatrixRTC mode both sides use; the default is compatibility mode. */
+  mode?: RtcMode;
   hostFlows: Flow[];
   guestFlows: Flow[];
 }[] = [
@@ -51,8 +54,19 @@ const cases: {
     guestFlows: ["cs-api"],
   },
   {
+    // In compatibility mode both publish a membership state event, so both
+    // must keep the legacy participant identity that clients predating MSC4195
+    // expect, which only the JWT service assigns.
     hostShape: "both",
     guestShape: "both",
+    hostFlows: ["service-legacy"],
+    guestFlows: ["service-legacy"],
+  },
+  {
+    // In Matrix 2.0 mode nobody expects a legacy identity, so the CS API wins.
+    hostShape: "both",
+    guestShape: "both",
+    mode: "2_0",
     hostFlows: ["cs-api"],
     guestFlows: ["cs-api"],
   },
@@ -64,8 +78,8 @@ const cases: {
   },
 ];
 
-for (const { hostShape, guestShape, hostFlows, guestFlows } of cases) {
-  test(`One to one call with ${hostShape} host and ${guestShape} guest transport`, async ({
+for (const { hostShape, guestShape, mode, hostFlows, guestFlows } of cases) {
+  test(`One to one call with ${hostShape} host and ${guestShape} guest transport${mode === "2_0" ? " in Matrix 2.0 mode" : ""}`, async ({
     browser,
     page,
     browserName,
@@ -76,7 +90,7 @@ for (const { hostShape, guestShape, hostFlows, guestFlows } of cases) {
     await advertiseTransport(page, shapes[hostShape]);
     const hostRequests = recordAuthRequests(page);
     await page.goto("/");
-    await SpaHelpers.createCall(page, "Androl", "HelloCall", true);
+    await SpaHelpers.createCall(page, "Androl", "HelloCall", true, mode);
     const inviteLink = await SpaHelpers.getCallInviteLink(page);
 
     // The guest joins.
@@ -84,7 +98,12 @@ for (const { hostShape, guestShape, hostFlows, guestFlows } of cases) {
     const guestPage = await guestContext.newPage();
     await advertiseTransport(guestPage, shapes[guestShape]);
     const guestRequests = recordAuthRequests(guestPage);
-    await SpaHelpers.joinCallFromInviteLink(guestPage, inviteLink, "Pevara");
+    await SpaHelpers.joinCallFromInviteLink(
+      guestPage,
+      inviteLink,
+      "Pevara",
+      mode,
+    );
 
     // Wait for the call to connect and render.
     await SpaHelpers.expectVideoTilesCount(page, 2);
diff --git a/src/livekit/auth/index.test.ts b/src/livekit/auth/index.test.ts
index 015e0b036..6112e4caf 100644
--- a/src/livekit/auth/index.test.ts
+++ b/src/livekit/auth/index.test.ts
@@ -21,6 +21,7 @@ import { delegateDelayedLeave, getSFUConfig } from ".";
 import { mocked } from "storybook/test";
 import { ConnectionError, MatrixError } from "matrix-js-sdk";
 import { NoMatrix2AuthorizationService } from "../../utils/errors";
+import { MatrixRTCMode } from "../../config/ConfigOptions";
 import { type CallMembershipIdentityParts } from "matrix-js-sdk/lib/matrixrtc/EncryptionManager";
 
 vi.mock("./openID", () => ({ getSFUConfig: vi.fn() }));
@@ -83,6 +84,7 @@ describe("getSFUConfig", () => {
     membership,
     serverName: "example.org",
     role: "subscriber" as const,
+    matrixRTCMode: MatrixRTCMode.Matrix_2_0,
     roomId,
     slotId,
     logger,
@@ -169,6 +171,53 @@ describe("getSFUConfig", () => {
     expect(openID.getSFUConfig).not.toHaveBeenCalled();
   });
 
+  it("uses OpenID when publishing in compatibility mode with url + livekit_service_url transport", async () => {
+    // Subscribers predating MSC4195 expect a legacy participant identity from
+    // anyone advertising a state event, which only the JWT service assigns
+    expect(
+      await getSFUConfig({
+        ...defaultParams,
+        transport: urlAndServiceUrlTransport,
+        role: "publisher",
+        matrixRTCMode: MatrixRTCMode.Compatibility,
+      }),
+    ).toEqual(
+      expect.objectContaining({
+        jwt: openIDJWTToken,
+        livekitAlias: "via OpenID",
+      }),
+    );
+    expect(client._unstable_getLivekitToken).not.toHaveBeenCalled();
+    expect(openID.getSFUConfig).toHaveBeenCalledWith(
+      expect.objectContaining({ role: "publisher" }),
+    );
+  });
+
+  it("uses CS API when publishing in compatibility mode with url transport", async () => {
+    expect(
+      await getSFUConfig({
+        ...defaultParams,
+        transport: urlTransport,
+        role: "publisher",
+        matrixRTCMode: MatrixRTCMode.Compatibility,
+      }),
+    ).toEqual(expect.objectContaining({ jwt: csApiJWTToken }));
+    expect(client._unstable_getLivekitToken).toHaveBeenCalled();
+    expect(openID.getSFUConfig).not.toHaveBeenCalled();
+  });
+
+  it("uses CS API when subscribing in compatibility mode with url + livekit_service_url transport", async () => {
+    expect(
+      await getSFUConfig({
+        ...defaultParams,
+        transport: urlAndServiceUrlTransport,
+        matrixRTCMode: MatrixRTCMode.Compatibility,
+      }),
+    ).toEqual(expect.objectContaining({ jwt: csApiJWTToken }));
+    expect(client._unstable_getLivekitToken).toHaveBeenCalled();
+    expect(openID.getSFUConfig).not.toHaveBeenCalled();
+  });
+
   it("does not fall back to OpenID on connection error", async () => {
     const client_ = {
       ...client,
@@ -198,6 +247,7 @@ describe("delegateDelayedLeave", () => {
     roomId,
     slotId,
     delayId: "delay123",
+    matrixRTCMode: MatrixRTCMode.Matrix_2_0,
     logger,
   };
 
@@ -236,6 +286,23 @@ describe("delegateDelayedLeave", () => {
     expect(openID.getSFUConfig).not.toHaveBeenCalled();
   });
 
+  it("uses OpenID in compatibility mode with url + livekit_service_url transport", async () => {
+    // Must match the flow that got the token, so the identities line up
+    await delegateDelayedLeave({
+      ...defaultParams,
+      transport: urlAndServiceUrlTransport,
+      matrixRTCMode: MatrixRTCMode.Compatibility,
+    });
+    expect(client._unstable_delegateDelayedLeave).not.toHaveBeenCalled();
+    expect(openID.getSFUConfig).toHaveBeenCalledWith(
+      expect.objectContaining({
+        role: "publisher",
+        delayId: "delay123",
+        delayEndpointBaseUrl: client.baseUrl,
+      }),
+    );
+  });
+
   it("does not fall back to OpenID with url + livekit_service_url transport", async () => {
     client._unstable_delegateDelayedLeave.mockRejectedValueOnce(
       unsupportedError,
diff --git a/src/livekit/auth/index.ts b/src/livekit/auth/index.ts
index c535e72f5..20258c81d 100644
--- a/src/livekit/auth/index.ts
+++ b/src/livekit/auth/index.ts
@@ -14,6 +14,7 @@ import * as openID from "./openID";
 import * as csApi from "./csApi";
 import { type SFUConfig } from "./types";
 import { NoMatrix2AuthorizationService } from "../../utils/errors";
+import { MatrixRTCMode } from "../../config/ConfigOptions";
 
 export type { ClientOpenIDParts } from "./openID";
 export type { ClientGetTokenParts, ClientDelegationParts } from "./csApi";
@@ -66,6 +67,11 @@ export interface GetSFUConfigParams {
    * Whether we want to publish or only subscribe on the {@link transport}.
    */
   role: "publisher" | "subscriber";
+  /**
+   * The MatrixRTC mode, which decides the format of our membership event and
+   * so the participant identity a publisher must have.
+   */
+  matrixRTCMode: MatrixRTCMode;
   logger: Logger;
 }
 
@@ -80,52 +86,51 @@ export async function getSFUConfig({
   roomId,
   slotId,
   role,
+  matrixRTCMode,
   logger,
 }: GetSFUConfigParams): Promise<SFUConfig> {
-  if ("url" in transport) {
-    try {
-      return await csApi.getSFUConfig({
-        client,
-        membership,
-        url: transport.url,
-        serverName,
-        roomId,
-        slotId,
-      });
-    } catch (e) {
-      if (isEndpointUnsupported(e)) {
-        // Publishers should never fall back. If a homeserver advertises a `url`
-        // but doesn't support MSC4195 itself, that's a misconfiguration which
-        // the admin should know about so they can prepare for the future
-        // deprecation of `livekit_service_url`.
-        const mayFallBack =
-          role === "subscriber" && "livekit_service_url" in transport;
-        if (mayFallBack) {
-          logger.warn(
-            `Homeserver does not support the MSC4195 get_token endpoint, falling back to the OpenID flow with service ${transport.livekit_service_url}`,
-          );
-          // Fall through
-        } else {
-          logger.error(
-            `Homeserver does not support the MSC4195 get_token endpoint, cannot get token for transport ${transport.url}`,
-          );
-          throw new NoMatrix2AuthorizationService(e as Error);
-        }
-      } else {
-        throw e;
-      }
-    }
-  }
+  const viaOpenID = async (serviceUrl: string): Promise<SFUConfig> =>
+    await openID.getSFUConfig({
+      client,
+      membership,
+      serviceUrl,
+      roomId,
+      slotId,
+      role,
+      logger,
+    });
 
-  return await openID.getSFUConfig({
-    client,
-    membership,
-    serviceUrl: transport.livekit_service_url,
-    roomId,
-    slotId,
-    role,
-    logger,
-  });
+  const flow = chooseAuthFlow(transport, role, matrixRTCMode);
+  if (flow.kind === "openID") return await viaOpenID(flow.serviceUrl);
+
+  try {
+    return await csApi.getSFUConfig({
+      client,
+      membership,
+      url: flow.url,
+      serverName,
+      roomId,
+      slotId,
+    });
+  } catch (e) {
+    if (!isEndpointUnsupported(e)) throw e;
+    // Publishers should never fall back. If a homeserver advertises a `url`
+    // but doesn't support MSC4195 itself, that's a misconfiguration which
+    // the admin should know about so they can prepare for the future
+    // deprecation of `livekit_service_url`.
+    const mayFallBack =
+      role === "subscriber" && "livekit_service_url" in transport;
+    if (!mayFallBack) {
+      logger.error(
+        `Homeserver does not support the MSC4195 get_token endpoint, cannot get token for transport ${flow.url}`,
+      );
+      throw new NoMatrix2AuthorizationService(e as Error);
+    }
+    logger.warn(
+      `Homeserver does not support the MSC4195 get_token endpoint, falling back to the OpenID flow with service ${transport.livekit_service_url}`,
+    );
+    return await viaOpenID(transport.livekit_service_url);
+  }
 }
 
 export interface DelegateDelayedLeaveParams {
@@ -154,6 +159,10 @@ export interface DelegateDelayedLeaveParams {
    * The delay ID of the leave event to be delegated.
    */
   delayId: string;
+  /**
+   * The MatrixRTC mode, which decides the format of our membership event.
+   */
+  matrixRTCMode: MatrixRTCMode;
   logger: Logger;
 }
 
@@ -168,17 +177,19 @@ export async function delegateDelayedLeave({
   roomId,
   slotId,
   delayId,
+  matrixRTCMode,
   logger,
 }: DelegateDelayedLeaveParams): Promise<void> {
   // It's important that we use the same flow (CS API or OpenID) as whatever we
   // would've used to get a JWT token for this transport, since the participant
   // identity computed by the service needs to match.
-  if ("url" in transport) {
+  const flow = chooseAuthFlow(transport, "publisher", matrixRTCMode);
+  if (flow.kind === "csApi") {
     try {
       await csApi.delegateDelayedLeave({
         client,
         membership,
-        url: transport.url,
+        url: flow.url,
         roomId,
         slotId,
         delayId,
@@ -196,7 +207,7 @@ export async function delegateDelayedLeave({
     await openID.getSFUConfig({
       client,
       membership,
-      serviceUrl: transport.livekit_service_url,
+      serviceUrl: flow.serviceUrl,
       roomId,
       slotId,
       role: "publisher",
@@ -206,3 +217,40 @@ export async function delegateDelayedLeave({
     });
   }
 }
+
+/**
+ * The flow with which the local member authenticates against a transport.
+ */
+export type AuthFlow =
+  | { kind: "csApi"; url: string }
+  | { kind: "openID"; serviceUrl: string };
+
+/**
+ * Chooses between the MSC4195 CS API and the legacy OpenID flow against the
+ * transport's JWT service.
+ *
+ * Only the JWT service's `/sfu/get` endpoint assigns the legacy participant
+ * identity that clients predating MSC4195 expect from anyone advertising a
+ * membership state event, which is what compatibility mode sends. So a
+ * publisher in compatibility mode keeps using the JWT service wherever the
+ * transport still offers one, even if it also has a `url`. Subscribers may use
+ * the CS API regardless, as nobody matches their identity.
+ * @param transport The transport to authenticate against.
+ * @param role Whether we want to publish or only subscribe on the transport.
+ * @param matrixRTCMode The MatrixRTC mode, which decides the format of our
+ *   membership event.
+ */
+export function chooseAuthFlow(
+  transport: UnstableLivekitTransport,
+  role: "publisher" | "subscriber",
+  matrixRTCMode: MatrixRTCMode,
+): AuthFlow {
+  if ("url" in transport) {
+    const useCsApi =
+      !("livekit_service_url" in transport) ||
+      role === "subscriber" ||
+      matrixRTCMode === MatrixRTCMode.Matrix_2_0;
+    if (useCsApi) return { kind: "csApi", url: transport.url };
+  }
+  return { kind: "openID", serviceUrl: transport.livekit_service_url };
+}
diff --git a/src/settings/DeveloperSettingsTab.tsx b/src/settings/DeveloperSettingsTab.tsx
index 3ef943ddf..42cc608c7 100644
--- a/src/settings/DeveloperSettingsTab.tsx
+++ b/src/settings/DeveloperSettingsTab.tsx
@@ -530,6 +530,7 @@ export const DeveloperSettingsTab: FC<Props> = ({
                 roomId,
                 slotId: "org.example.fake-slot#room",
                 role: "publisher",
+                matrixRTCMode: effectiveMatrixRTCMode,
                 logger,
               });
               setCustomLivekitUrlUpdateError(null);
@@ -540,7 +541,13 @@ export const DeveloperSettingsTab: FC<Props> = ({
               );
             }
           },
-          [customTransportTextBuffer, setCustomTransport, client, roomId],
+          [
+            customTransportTextBuffer,
+            setCustomTransport,
+            client,
+            roomId,
+            effectiveMatrixRTCMode,
+          ],
         )}
         value={customTransportTextBuffer ?? ""}
         onChange={useCallback(
diff --git a/src/state/CallViewModel/CallViewModel.ts b/src/state/CallViewModel/CallViewModel.ts
index 169abb98c..5821204a1 100644
--- a/src/state/CallViewModel/CallViewModel.ts
+++ b/src/state/CallViewModel/CallViewModel.ts
@@ -575,6 +575,7 @@ export function createCallViewModel$(
       client,
       matrixRoom.roomId,
       matrixRTCSession.slotId,
+      matrixRTCMode,
       mediaDevices,
       trackProcessorState$,
       livekitKeyProvider,
@@ -665,6 +666,7 @@ export function createCallViewModel$(
       ).pipe(map(([delayId]) => delayId ?? null)),
       matrixRTCSession.delayId ?? null,
     ),
+    matrixRTCMode,
     logger: logger.getChild(`[${Date.now()}]`),
   });
 
diff --git a/src/state/CallViewModel/CallViewModelTestUtils.ts b/src/state/CallViewModel/CallViewModelTestUtils.ts
index 93c190ace..6ef3e9f8d 100644
--- a/src/state/CallViewModel/CallViewModelTestUtils.ts
+++ b/src/state/CallViewModel/CallViewModelTestUtils.ts
@@ -230,6 +230,7 @@ export function withCallViewModel(mode: MatrixRTCMode) {
                 client: room.client,
                 roomId: room.roomId,
                 slotId: "m.call#ROOM",
+                matrixRTCMode: mode,
                 livekitRoomFactory,
               },
               logger,
diff --git a/src/state/CallViewModel/localMember/LocalMember.test.ts b/src/state/CallViewModel/localMember/LocalMember.test.ts
index 2d721f7d6..273b6c8f3 100644
--- a/src/state/CallViewModel/localMember/LocalMember.test.ts
+++ b/src/state/CallViewModel/localMember/LocalMember.test.ts
@@ -346,21 +346,27 @@ describe("LocalMembership", () => {
     .mockResolvedValue();
   afterEach(() => delegationSpy.mockClear());
 
+  // The transport has both a `url` and a `livekit_service_url`. In Matrix 2.0
+  // mode we publish through the CS API, so the homeserver delegates; in
+  // compatibility mode we publish through the JWT service, so that delegates.
   it.each([
-    ["no", null, timings],
+    ["no", MatrixRTCMode.Compatibility, null, timings],
+    ["no", MatrixRTCMode.Matrix_2_0, null, timings],
     [
       "homeserver",
+      MatrixRTCMode.Matrix_2_0,
       "https://matrix.example.org/_matrix/client/unstable/io.element.msc4195/rtc/livekit/delegate_delayed_leave",
       delegatedTimings,
     ],
     [
       "transport",
+      MatrixRTCMode.Compatibility,
       "https://jwt.example.org/delegate_delayed_leave",
       delegatedTimings,
     ],
   ])(
-    "joins session with %s delegation support",
-    async (_serviceName, delegationUrl, delayedLeaveTimings) => {
+    "joins session with %s delegation support in %s mode",
+    async (_serviceName, matrixRTCMode, delegationUrl, delayedLeaveTimings) => {
       const scope = testScope();
       const joinMatrixRTC = vi.fn();
       const delayId$ = new BehaviorSubject<string | null>(null);
@@ -377,6 +383,7 @@ describe("LocalMembership", () => {
         joinMatrixRTC,
         localTransport$: constant(mockTransportLocator),
         delayId$,
+        matrixRTCMode,
       });
 
       localMembership.requestJoinAndPublish();
@@ -403,6 +410,7 @@ describe("LocalMembership", () => {
             transport: mockTransport,
             roomId: "!test-room-id:example.org",
             delayId,
+            matrixRTCMode,
             logger: expect.anything(),
           });
 
diff --git a/src/state/CallViewModel/localMember/LocalMember.ts b/src/state/CallViewModel/localMember/LocalMember.ts
index 244c728dc..b4af36b58 100644
--- a/src/state/CallViewModel/localMember/LocalMember.ts
+++ b/src/state/CallViewModel/localMember/LocalMember.ts
@@ -82,6 +82,7 @@ import {
   type ClientDelegationParts,
   delegateDelayedLeave,
   type ClientOpenIDParts,
+  chooseAuthFlow,
   type TransportLocator,
 } from "../../../livekit/auth";
 
@@ -164,6 +165,8 @@ interface Props {
   hostBridge: HostBridge;
   baseUrl: string;
   delayId$: Behavior<string | null>;
+  /** The MatrixRTC mode, which decides the format of our membership event. */
+  matrixRTCMode: MatrixRTCMode;
   logger: Logger;
 }
 
@@ -211,6 +214,7 @@ export const createLocalMembership$ = ({
   hostBridge,
   ownMembershipIdentity,
   delayId$,
+  matrixRTCMode,
 }: Props): {
   /**
    * This request to start audio and video tracks.
@@ -312,17 +316,17 @@ export const createLocalMembership$ = ({
   const joinParams$ = scope.behavior(
     localTransport$.pipe(
       switchMap(async ({ transport }) => {
-        const transportSupportsDelegation =
-          "livekit_service_url" in transport &&
-          (await checkDelegationSupport(
-            transport.livekit_service_url + "/delegate_delayed_leave",
-            `transport ${transport.livekit_service_url}`,
-          ));
-        return {
-          transport,
-          delegationSupported:
-            transportSupportsDelegation || (await homeserverSupportsDelegation),
-        };
+        // Delegation goes through whichever service authenticates us as a
+        // publisher, so only that service's support counts
+        const flow = chooseAuthFlow(transport, "publisher", matrixRTCMode);
+        const delegationSupported =
+          flow.kind === "openID"
+            ? await checkDelegationSupport(
+                flow.serviceUrl + "/delegate_delayed_leave",
+                `transport ${flow.serviceUrl}`,
+              )
+            : await homeserverSupportsDelegation;
+        return { transport, delegationSupported };
       }),
     ),
     null,
@@ -731,6 +735,7 @@ export const createLocalMembership$ = ({
             slotId: matrixRTCSession.slotId,
             roomId,
             delayId,
+            matrixRTCMode,
             logger,
           });
           logger.info("Delayed leave successfully delegated");
diff --git a/src/state/CallViewModel/remoteMembers/Connection.test.ts b/src/state/CallViewModel/remoteMembers/Connection.test.ts
index bdab8e7af..632122a3f 100644
--- a/src/state/CallViewModel/remoteMembers/Connection.test.ts
+++ b/src/state/CallViewModel/remoteMembers/Connection.test.ts
@@ -42,6 +42,7 @@ import {
 } from "./Connection.ts";
 import { ObservableScope } from "../../ObservableScope.ts";
 import { FailToGetOpenIdToken } from "../../../utils/errors.ts";
+import { MatrixRTCMode } from "../../../config/ConfigOptions.ts";
 import { testJWTToken } from "../../../utils/test-fixtures.ts";
 import { mockRemoteParticipant, ownMemberMock } from "../../../utils/test.ts";
 import {
@@ -123,6 +124,7 @@ function setupRemoteConnection(): Connection {
     client,
     roomId: ROOM_ID,
     slotId: SLOT_ID,
+    matrixRTCMode: MatrixRTCMode.Matrix_2_0,
     role: "subscriber",
     transport,
     serverName: "m.localhost",
@@ -172,6 +174,7 @@ describe("Start connection states", () => {
       client,
       roomId: ROOM_ID,
       slotId: SLOT_ID,
+      matrixRTCMode: MatrixRTCMode.Matrix_2_0,
       role: "subscriber",
       transport,
       serverName: "m.localhost",
@@ -192,6 +195,7 @@ describe("Start connection states", () => {
       client,
       roomId: ROOM_ID,
       slotId: SLOT_ID,
+      matrixRTCMode: MatrixRTCMode.Matrix_2_0,
       role: "subscriber",
       transport,
       serverName: "m.localhost",
@@ -247,6 +251,7 @@ describe("Start connection states", () => {
       client,
       roomId: ROOM_ID,
       slotId: SLOT_ID,
+      matrixRTCMode: MatrixRTCMode.Matrix_2_0,
       role: "subscriber",
       transport,
       serverName: "m.localhost",
@@ -311,6 +316,7 @@ describe("Start connection states", () => {
       client,
       roomId: ROOM_ID,
       slotId: SLOT_ID,
+      matrixRTCMode: MatrixRTCMode.Matrix_2_0,
       role: "subscriber",
       transport,
       serverName: "m.localhost",
@@ -561,6 +567,7 @@ describe("remote track logging", () => {
         client,
         roomId: ROOM_ID,
         slotId: SLOT_ID,
+        matrixRTCMode: MatrixRTCMode.Matrix_2_0,
         role: "subscriber",
         transport,
         serverName: "m.localhost",
diff --git a/src/state/CallViewModel/remoteMembers/Connection.ts b/src/state/CallViewModel/remoteMembers/Connection.ts
index 7e94b39f1..cbdffcbde 100644
--- a/src/state/CallViewModel/remoteMembers/Connection.ts
+++ b/src/state/CallViewModel/remoteMembers/Connection.ts
@@ -44,12 +44,15 @@ import {
   type ClientOpenIDParts,
   type SFUConfig,
 } from "../../../livekit/auth";
+import { type MatrixRTCMode } from "../../../config/ConfigOptions.ts";
 
 export interface ConnectionOpts {
   /** The identity parts to use on this connection */
   ownMembershipIdentity: CallMembershipIdentityParts;
   /** Whether we want to publish or only subscribe on this connection. */
   role: "publisher" | "subscriber";
+  /** The MatrixRTC mode, which decides the format of our membership event. */
+  matrixRTCMode: MatrixRTCMode;
   /** The media transport to connect to. */
   transport: UnstableLivekitTransport;
   /** The name of the homeserver to which the {@link transport} belongs. */
@@ -138,6 +141,7 @@ export class Connection {
   private readonly client: ClientGetTokenParts & ClientOpenIDParts;
   private readonly roomId: string;
   private readonly slotId: string;
+  private readonly matrixRTCMode: MatrixRTCMode;
   private readonly logger: Logger;
   private readonly ownMembershipIdentity: CallMembershipIdentityParts;
   /**
@@ -151,6 +155,7 @@ export class Connection {
     this.ownMembershipIdentity = opts.ownMembershipIdentity;
     this.roomId = opts.roomId;
     this.slotId = opts.slotId;
+    this.matrixRTCMode = opts.matrixRTCMode;
     this.logger = logger.getChild(
       `[Connection ${JSON.stringify(opts.transport)}]`,
     );
@@ -394,6 +399,7 @@ export class Connection {
       serverName: this.serverName,
       roomId: this.roomId,
       slotId: this.slotId,
+      matrixRTCMode: this.matrixRTCMode,
       logger: this.logger,
     });
   }
diff --git a/src/state/CallViewModel/remoteMembers/ConnectionFactory.ts b/src/state/CallViewModel/remoteMembers/ConnectionFactory.ts
index e5240f096..39ac35706 100644
--- a/src/state/CallViewModel/remoteMembers/ConnectionFactory.ts
+++ b/src/state/CallViewModel/remoteMembers/ConnectionFactory.ts
@@ -39,6 +39,7 @@ import {
   type ClientGetTokenParts,
   type ClientOpenIDParts,
 } from "../../../livekit/auth";
+import { type MatrixRTCMode } from "../../../config/ConfigOptions.ts";
 
 // TODO evaluate if this should be done like the Publisher Factory
 export interface ConnectionFactory {
@@ -61,6 +62,7 @@ export class ECConnectionFactory implements ConnectionFactory {
    * @param client - The OpenID client parts for authentication, needed to get openID and JWT tokens.
    * @param roomId - The ID of the Matrix room in which the session takes place.
    * @param slotId - The ID of the MatrixRTC slot in which the session takes place.
+   * @param matrixRTCMode - The MatrixRTC mode, which decides the format of our membership event.
    * @param devices - Used for video/audio out/in capture options.
    * @param processorState$ - Effects like background blur (only for publishing connection?)
    * @param livekitKeyProvider - Optional key provider for end-to-end encryption.
@@ -71,6 +73,7 @@ export class ECConnectionFactory implements ConnectionFactory {
     private client: ClientGetTokenParts & ClientOpenIDParts,
     private readonly roomId: string,
     private readonly slotId: string,
+    private readonly matrixRTCMode: MatrixRTCMode,
     private devices: MediaDevices,
     private processorState$: Behavior<ProcessorState>,
     livekitKeyProvider: BaseKeyProvider | undefined,
@@ -117,6 +120,7 @@ export class ECConnectionFactory implements ConnectionFactory {
       {
         roomId: this.roomId,
         slotId: this.slotId,
+        matrixRTCMode: this.matrixRTCMode,
         role,
         transport,
         serverName,
diff --git a/src/state/CallViewModel/remoteMembers/ECConnectionFactory.test.ts b/src/state/CallViewModel/remoteMembers/ECConnectionFactory.test.ts
index be6c149f4..0a9310f82 100644
--- a/src/state/CallViewModel/remoteMembers/ECConnectionFactory.test.ts
+++ b/src/state/CallViewModel/remoteMembers/ECConnectionFactory.test.ts
@@ -36,6 +36,7 @@ import {
   cameraCodec,
 } from "../../../settings/settings.ts";
 import { testJWTToken } from "../../../utils/test-fixtures.ts";
+import { MatrixRTCMode } from "../../../config/ConfigOptions.ts";
 
 // At the top of your test file, after imports
 vi.mock("livekit-client", async (importOriginal) => {
@@ -84,6 +85,7 @@ describe("ECConnectionFactory - Audio inputs options", () => {
         mockClient,
         "!roomid:example.org",
         "m.call#ROOM",
+        MatrixRTCMode.Matrix_2_0,
         mockMediaDevices({}),
         new BehaviorSubject<ProcessorState>({
           supported: true,
@@ -129,6 +131,7 @@ describe("ECConnectionFactory - ControlledAudioDevice", () => {
         mockClient,
         "!roomid:example.org",
         "m.call#ROOM",
+        MatrixRTCMode.Matrix_2_0,
         mockMediaDevices({
           audioOutput: {
             available$: constant(new Map<never, never>()),
@@ -173,6 +176,7 @@ describe("ECConnectionFactory - Camera quality settings", () => {
       mockClient,
       "!roomid:example.org",
       "m.call#ROOM",
+      MatrixRTCMode.Matrix_2_0,
       mockMediaDevices({}),
       new BehaviorSubject<ProcessorState>({
         supported: true,
@@ -213,6 +217,7 @@ describe("ECConnectionFactory - Camera quality settings", () => {
       mockClient,
       "!roomid:example.org",
       "m.call#ROOM",
+      MatrixRTCMode.Matrix_2_0,
       mockMediaDevices({}),
       new BehaviorSubject<ProcessorState>({
         supported: true,
@@ -254,6 +259,7 @@ describe("ECConnectionFactory - Camera quality settings", () => {
       mockClient,
       "!roomid:example.org",
       "m.call#ROOM",
+      MatrixRTCMode.Matrix_2_0,
       mockMediaDevices({}),
       new BehaviorSubject<ProcessorState>({
         supported: true,
diff --git a/src/state/CallViewModel/remoteMembers/integration.test.ts b/src/state/CallViewModel/remoteMembers/integration.test.ts
index bf90e9eb4..b610447d9 100644
--- a/src/state/CallViewModel/remoteMembers/integration.test.ts
+++ b/src/state/CallViewModel/remoteMembers/integration.test.ts
@@ -38,6 +38,7 @@ import { createConnectionMap$ } from "./ConnectionMap.ts";
 import { membershipsAndTransports$ } from "../../SessionBehaviors.ts";
 import { localRtcMember, testJWTToken } from "../../../utils/test-fixtures.ts";
 import { deepCompare } from "matrix-js-sdk/lib/utils";
+import { MatrixRTCMode } from "../../../config/ConfigOptions.ts";
 
 // Test the integration of ConnectionMap and MatrixLivekitMembers
 
@@ -75,6 +76,7 @@ beforeEach(() => {
     mockClient,
     "!roomid:example.org",
     "m.call#ROOM",
+    MatrixRTCMode.Matrix_2_0,
     mockMediaDevices({}),
     new BehaviorSubject<ProcessorState>({
       supported: true,