diff --git a/package.json b/package.json
index 0ba5892d1f..0bbd0283dd 100644
--- a/package.json
+++ b/package.json
@@ -130,7 +130,7 @@
         "maplibre-gl": "^5.0.0",
         "matrix-encrypt-attachment": "^1.0.3",
         "matrix-js-sdk": "github:matrix-org/matrix-js-sdk#develop",
-        "matrix-widget-api": "^1.14.0",
+        "matrix-widget-api": "^1.15.0",
         "memoize-one": "^6.0.0",
         "mime": "^4.0.4",
         "oidc-client-ts": "^3.0.1",
diff --git a/playwright/e2e/voip/element-call.spec.ts b/playwright/e2e/voip/element-call.spec.ts
index c12226928e..7c2494d2ae 100644
--- a/playwright/e2e/voip/element-call.spec.ts
+++ b/playwright/e2e/voip/element-call.spec.ts
@@ -13,6 +13,7 @@ import { SettingLevel } from "../../../src/settings/SettingLevel";
 import { test, expect } from "../../element-web-test";
 import type { Credentials } from "../../plugins/homeserver";
 import { Bot } from "../../pages/bot";
+import { isDendrite } from "../../plugins/homeserver/dendrite";
 
 // Load a copy of our fake Element Call app, and the latest widget API.
 // The fake call app does *just* enough to convince Element Web that a call is ongoing
@@ -578,4 +579,84 @@ test.describe("Element Call", () => {
             await openAndJoinCall(page, true);
         });
     });
+
+    test.describe("Widget leak bug reproduction", { tag: ["@no-firefox", "@no-webkit"] }, () => {
+        test.skip(isDendrite, "No need to test on other HS, this is a client bug reproduction");
+        test.use({
+            config: {
+                features: {
+                    feature_video_rooms: true,
+                    feature_element_call_video_rooms: true,
+                },
+            },
+        });
+
+        const fakeCallClientSend = readFile("playwright/sample-files/fake-element-call-with-send.html", "utf-8");
+
+        let charlie: Bot;
+        test.use({
+            room: async ({ page, app, user, homeserver, bot }, use) => {
+                charlie = new Bot(page, homeserver, { displayName: "Charlie" });
+                await charlie.prepareClient();
+                const roomId = await app.client.createRoom({
+                    name: "VideoRoom",
+                    invite: [bot.credentials.userId, charlie.credentials.userId],
+                    creation_content: {
+                        type: "org.matrix.msc3417.call",
+                    },
+                });
+                await app.client.createRoom({
+                    name: "OtherRoom",
+                });
+                await use({ roomId });
+            },
+        });
+
+        test.beforeEach(async ({ page, user, app }) => {
+            // use a specific widget to reproduce the bug.
+            // Mock a widget page. We use a fake version of Element Call here.
+            // We should match on things after .html as these widgets get a ton of extra params.
+            await page.route(/\/widget-with-send.html.+/, async (route) => {
+                await route.fulfill({
+                    status: 200,
+                    // Do enough to
+                    body: (await fakeCallClientSend).replace("widgetCodeHere", await widgetApi),
+                });
+            });
+            await app.settings.setValue(
+                "Developer.elementCallUrl",
+                null,
+                SettingLevel.DEVICE,
+                new URL("/widget-with-send.html#", page.url()).toString(),
+            );
+        });
+
+        test("Switching rooms should not leak widgets", async ({ page, user, room, app }) => {
+            await app.viewRoomByName("VideoRoom");
+
+            await expect(page.getByRole("heading", { name: "Approve widget permissions" })).toBeVisible();
+            // approve
+            await page.getByTestId("dialog-primary-button").click();
+
+            // Switch back and forth a few times to trigger the bug.
+
+            await app.viewRoomByName("OtherRoom");
+            await app.viewRoomByName("VideoRoom");
+            await app.viewRoomByName("OtherRoom");
+            await app.viewRoomByName("VideoRoom");
+
+            // For this test we want to display the chat area alongside the widget
+            await page.getByRole("button", { name: "Chat" }).click();
+
+            await page
+                .locator('iframe[title="Element Call"]')
+                .contentFrame()
+                .getByRole("button", { name: "Send Room Message" })
+                .click();
+
+            const messageSent = await page.getByText("I sent this once!!").count();
+
+            expect(messageSent).toBe(1);
+        });
+    });
 });
diff --git a/playwright/sample-files/fake-element-call-with-send.html b/playwright/sample-files/fake-element-call-with-send.html
new file mode 100644
index 0000000000..c7fb2fdcbc
--- /dev/null
+++ b/playwright/sample-files/fake-element-call-with-send.html
@@ -0,0 +1,53 @@
+<!doctype html>
+<style>
+    body {
+        background: rgb(139, 192, 253);
+    }
+</style>
+
+<!-- element-call.spec.ts will insert the widget API in this block -->
+<script>
+    widgetCodeHere;
+</script>
+
+<div>
+    <p>Fake Element Call</p>
+    <p>State: <span id="state">Loading</span></p>
+    <button id="send-button">Send Room Message</button>
+</div>
+
+<!-- Minimal fake implementation of Element Call. Just enough for testing the leagkin widgets.-->
+<script>
+    const stateIndicator = document.querySelector("#state");
+    const { WidgetApi, WidgetApiToWidgetAction, MatrixCapabilities } = mxwidgets();
+    const widgetId = new URLSearchParams(window.location.search).get("widgetId");
+    const params = new URLSearchParams(window.location.hash.slice(1));
+
+    const roomId = params.get("roomId");
+    const api = new WidgetApi(widgetId, "*");
+
+    document.querySelector("#send-button").onclick = async () => {
+        await api.sendRoomEvent(
+            "m.room.message",
+            { msgtype: "m.text", body: "I sent this once!!" },
+            roomId,
+            undefined,
+            undefined,
+            undefined,
+        );
+    };
+
+    api.requestCapability(MatrixCapabilities.AlwaysOnScreen);
+    api.requestCapability(`org.matrix.msc2762.timeline:${roomId}`);
+    api.requestCapabilityToSendMessage("m.text");
+
+    api.on("ready", (ev) => {
+        stateIndicator.innerHTML = "Ready";
+    });
+
+    // Start the messaging
+    api.start();
+
+    // If waitForIframeLoad is false, tell the client that we're good to go
+    api.sendContentLoaded();
+</script>
diff --git a/src/stores/widgets/ElementWidgetDriver.ts b/src/stores/widgets/ElementWidgetDriver.ts
index 010c777333..82da6c3d59 100644
--- a/src/stores/widgets/ElementWidgetDriver.ts
+++ b/src/stores/widgets/ElementWidgetDriver.ts
@@ -33,12 +33,14 @@ import {
     EventType,
     type IContent,
     MatrixError,
-    type MatrixEvent,
     Direction,
     THREAD_RELATION_TYPE,
     type SendDelayedEventResponse,
     type StateEvents,
     type TimelineEvents,
+    type Room,
+    type SendDelayedEventRequestOpts,
+    type MatrixClient,
 } from "matrix-js-sdk/src/matrix";
 import { logger } from "matrix-js-sdk/src/logger";
 import {
@@ -122,6 +124,7 @@ export class ElementWidgetDriver extends WidgetDriver {
             this.allowedCapabilities.add(`org.matrix.msc2762.timeline:${inRoomId}`);
             this.allowedCapabilities.add(MatrixCapabilities.MSC4157SendDelayedEvent);
             this.allowedCapabilities.add(MatrixCapabilities.MSC4157UpdateDelayedEvent);
+            this.allowedCapabilities.add(MatrixCapabilities.MSC4354SendStickyEvent);
 
             this.allowedCapabilities.add(
                 WidgetEventCapability.forStateEvent(EventDirection.Receive, EventType.RoomName).raw,
@@ -288,6 +291,13 @@ export class ElementWidgetDriver extends WidgetDriver {
         return allAllowed;
     }
 
+    private getSendEventTarget(roomId: string | null = null): { client: MatrixClient; roomId: string } {
+        const client = MatrixClientPeg.safeGet();
+        roomId = roomId || SdkContextClass.instance.roomViewStore.getRoomId() || null;
+        if (!roomId) throw new Error("No room specified and no room in RoomViewStore focus.");
+        return { client, roomId };
+    }
+
     public async sendEvent<K extends keyof StateEvents>(
         eventType: K,
         content: StateEvents[K],
@@ -306,10 +316,7 @@ export class ElementWidgetDriver extends WidgetDriver {
         stateKey: string | null = null,
         targetRoomId: string | null = null,
     ): Promise<ISendEventDetails> {
-        const client = MatrixClientPeg.get();
-        const roomId = targetRoomId || SdkContextClass.instance.roomViewStore.getRoomId();
-
-        if (!client || !roomId) throw new Error("Not in a room or not attached to a client");
+        const { client, roomId } = this.getSendEventTarget(targetRoomId);
 
         let r: { event_id: string } | null;
         if (stateKey !== null) {
@@ -348,6 +355,42 @@ export class ElementWidgetDriver extends WidgetDriver {
         return { roomId, eventId: r.event_id };
     }
 
+    /**
+     * @experimental Part of MSC4354
+     * @see {@link WidgetDriver#sendStickyEvent}
+     */
+    public async sendStickyEvent(
+        stickyDurationMs: number,
+        eventType: string,
+        content: unknown,
+        targetRoomId?: string | null,
+    ): Promise<ISendEventDetails> {
+        const { client, roomId } = this.getSendEventTarget(targetRoomId);
+
+        const r = await client._unstable_sendStickyEvent(
+            roomId,
+            stickyDurationMs,
+            null,
+            eventType as keyof TimelineEvents,
+            content as TimelineEvents[keyof TimelineEvents] & { msc4354_sticky_key: string },
+        );
+        return { roomId, eventId: r.event_id };
+    }
+
+    private getSendDelayedEventOpts(delay: number | null, parentDelayId: string | null): SendDelayedEventRequestOpts {
+        if (delay !== null) {
+            return {
+                delay,
+                ...(parentDelayId !== null && { parent_delay_id: parentDelayId }),
+            };
+        } else if (parentDelayId !== null) {
+            return {
+                parent_delay_id: parentDelayId,
+            };
+        }
+        throw new Error("Must provide at least one of delay or parentDelayId");
+    }
+
     /**
      * @experimental Part of MSC4140 & MSC4157
      * @see {@link WidgetDriver#sendDelayedEvent}
@@ -379,24 +422,8 @@ export class ElementWidgetDriver extends WidgetDriver {
         stateKey: string | null = null,
         targetRoomId: string | null = null,
     ): Promise<ISendDelayedEventDetails> {
-        const client = MatrixClientPeg.get();
-        const roomId = targetRoomId || SdkContextClass.instance.roomViewStore.getRoomId();
-
-        if (!client || !roomId) throw new Error("Not in a room or not attached to a client");
-
-        let delayOpts;
-        if (delay !== null) {
-            delayOpts = {
-                delay,
-                ...(parentDelayId !== null && { parent_delay_id: parentDelayId }),
-            };
-        } else if (parentDelayId !== null) {
-            delayOpts = {
-                parent_delay_id: parentDelayId,
-            };
-        } else {
-            throw new Error("Must provide at least one of delay or parentDelayId");
-        }
+        const { client, roomId } = this.getSendEventTarget(targetRoomId);
+        const delayOpts = this.getSendDelayedEventOpts(delay, parentDelayId);
 
         let r: SendDelayedEventResponse | null;
         if (stateKey !== null) {
@@ -425,13 +452,39 @@ export class ElementWidgetDriver extends WidgetDriver {
         };
     }
 
+    /**
+     * @experimental Part of MSC4354
+     * @see {@link WidgetDriver#sendStickyEvent}
+     */
+    public async sendDelayedStickyEvent(
+        delay: number | null,
+        parentDelayId: string | null,
+        stickyDurationMs: number,
+        eventType: string,
+        content: unknown,
+        targetRoomId?: string | null,
+    ): Promise<ISendDelayedEventDetails> {
+        const { client, roomId } = this.getSendEventTarget(targetRoomId);
+        const delayOpts = this.getSendDelayedEventOpts(delay, parentDelayId);
+
+        const r = await client._unstable_sendStickyDelayedEvent(
+            roomId,
+            stickyDurationMs,
+            delayOpts,
+            null,
+            eventType as keyof TimelineEvents,
+            content as TimelineEvents[keyof TimelineEvents] & { msc4354_sticky_key: string },
+        );
+        return { roomId, delayId: r.delay_id };
+    }
+
     /**
      * @experimental Part of MSC4140 & MSC4157
      */
     public async cancelScheduledDelayedEvent(delayId: string): Promise<void> {
         const client = MatrixClientPeg.get();
 
-        if (!client) throw new Error("Not in a room or not attached to a client");
+        if (!client) throw new Error("Not attached to a client");
 
         await client._unstable_cancelScheduledDelayedEvent(delayId);
     }
@@ -442,7 +495,7 @@ export class ElementWidgetDriver extends WidgetDriver {
     public async restartScheduledDelayedEvent(delayId: string): Promise<void> {
         const client = MatrixClientPeg.get();
 
-        if (!client) throw new Error("Not in a room or not attached to a client");
+        if (!client) throw new Error("Not attached to a client");
 
         await client._unstable_restartScheduledDelayedEvent(delayId);
     }
@@ -453,7 +506,7 @@ export class ElementWidgetDriver extends WidgetDriver {
     public async sendScheduledDelayedEvent(delayId: string): Promise<void> {
         const client = MatrixClientPeg.get();
 
-        if (!client) throw new Error("Not in a room or not attached to a client");
+        if (!client) throw new Error("Not attached to a client");
 
         await client._unstable_sendScheduledDelayedEvent(delayId);
     }
@@ -510,6 +563,38 @@ export class ElementWidgetDriver extends WidgetDriver {
         }
     }
 
+    /**
+     * Generator function that retrieves events for readRoomTimeline
+     * @param room The room to check the timeline of.
+     * @param eventType The event type to be read.
+     * @param msgtype The msgtype of the events to be read, if applicable/defined.
+     * @param stateKey The state key of the events to be read, if applicable/defined.
+     * @param limit The maximum number of events to retrieve. Will be zero to denote "as many as
+     * possible".
+     * @param since When null, retrieves the number of events specified by the "limit" parameter.
+     * Otherwise, the event ID at which only subsequent events will be returned, as many as specified
+     * in "limit".
+     * @returns A generator that emits events.
+     */
+    private *readRoomTimelineIterator(
+        room: Room,
+        eventType: string,
+        msgtype: string | undefined,
+        stateKey: string | undefined,
+        limit: number,
+        since: string | undefined,
+    ): Generator<IRoomEvent, void, void> {
+        let resultCount: number = 0;
+        const events = [...room.getLiveTimeline().getEvents()]; // timelines are most recent last
+        for (let ev = events.pop(); ev && resultCount < limit && ev.getId() !== since; ev = events.pop()) {
+            if (ev.getType() !== eventType) continue;
+            if (eventType === EventType.RoomMessage && msgtype && msgtype !== ev.getContent()["msgtype"]) continue;
+            if (stateKey !== undefined && ev.getStateKey() !== stateKey) continue;
+            yield ev.getEffectiveEvent() as IRoomEvent;
+            resultCount++;
+        }
+    }
+
     /**
      * Reads all events of the given type, and optionally `msgtype` (if applicable/defined),
      * the user has access to. The widget API will have already verified that the widget is
@@ -535,23 +620,9 @@ export class ElementWidgetDriver extends WidgetDriver {
         since: string | undefined,
     ): Promise<IRoomEvent[]> {
         limit = limit > 0 ? Math.min(limit, Number.MAX_SAFE_INTEGER) : Number.MAX_SAFE_INTEGER; // relatively arbitrary
-
         const room = MatrixClientPeg.safeGet().getRoom(roomId);
         if (room === null) return [];
-        const results: MatrixEvent[] = [];
-        const events = room.getLiveTimeline().getEvents(); // timelines are most recent last
-        for (let i = events.length - 1; i >= 0; i--) {
-            const ev = events[i];
-            if (results.length >= limit) break;
-            if (since !== undefined && ev.getId() === since) break;
-
-            if (ev.getType() !== eventType) continue;
-            if (eventType === EventType.RoomMessage && msgtype && msgtype !== ev.getContent()["msgtype"]) continue;
-            if (stateKey !== undefined && ev.getStateKey() !== stateKey) continue;
-            results.push(ev);
-        }
-
-        return results.map((e) => e.getEffectiveEvent() as IRoomEvent);
+        return [...this.readRoomTimelineIterator(room, eventType, msgtype, stateKey, limit, since)];
     }
 
     /**
diff --git a/src/stores/widgets/WidgetMessaging.ts b/src/stores/widgets/WidgetMessaging.ts
index 58abe5b34d..6731f1d1d9 100644
--- a/src/stores/widgets/WidgetMessaging.ts
+++ b/src/stores/widgets/WidgetMessaging.ts
@@ -508,6 +508,8 @@ export class WidgetMessaging extends TypedEventEmitter<WidgetMessagingEvent, Wid
         }
 
         this.emit(WidgetMessagingEvent.Stop, this.widgetApi);
+        this.widgetApi?.stop();
+        // XXX is the removeAllListeners necessary here?
         this.widgetApi?.removeAllListeners(); // Insurance against resource leaks
         this.widgetApi = null;
         this.iframe = null;
@@ -538,10 +540,8 @@ export class WidgetMessaging extends TypedEventEmitter<WidgetMessagingEvent, Wid
         });
     };
 
-    private onToDeviceMessage = async (payload: ReceivedToDeviceMessage): Promise<void> => {
-        const { message, encryptionInfo } = payload;
-        // TODO: Update the widget API to use a proper IToDeviceMessage instead of a IRoomEvent
-        await this.widgetApi?.feedToDevice(message as IRoomEvent, encryptionInfo != null);
+    private onToDeviceMessage = async ({ message, encryptionInfo }: ReceivedToDeviceMessage): Promise<void> => {
+        await this.widgetApi?.feedToDevice(message, encryptionInfo != null);
     };
 
     /**
diff --git a/test/test-utils/test-utils.ts b/test/test-utils/test-utils.ts
index 9757905882..d3d6e0bec1 100644
--- a/test/test-utils/test-utils.ts
+++ b/test/test-utils/test-utils.ts
@@ -308,6 +308,8 @@ export function createTestClient(): MatrixClient {
         _unstable_cancelScheduledDelayedEvent: jest.fn(),
         _unstable_restartScheduledDelayedEvent: jest.fn(),
         _unstable_sendScheduledDelayedEvent: jest.fn(),
+        _unstable_sendStickyEvent: jest.fn(),
+        _unstable_sendStickyDelayedEvent: jest.fn(),
 
         searchUserDirectory: jest.fn().mockResolvedValue({ limited: false, results: [] }),
         setDeviceVerified: jest.fn(),
diff --git a/test/unit-tests/stores/widgets/ElementWidgetDriver-test.ts b/test/unit-tests/stores/widgets/ElementWidgetDriver-test.ts
index 0499ba5033..0f3602bd3a 100644
--- a/test/unit-tests/stores/widgets/ElementWidgetDriver-test.ts
+++ b/test/unit-tests/stores/widgets/ElementWidgetDriver-test.ts
@@ -131,6 +131,7 @@ describe("ElementWidgetDriver", () => {
             "org.matrix.msc3819.receive.to_device:m.call.replaces",
             "org.matrix.msc4157.send.delayed_event",
             "org.matrix.msc4157.update_delayed_event",
+            "org.matrix.msc4354.send_sticky_event",
             // RTC decline events (send/receive, unstable/stable)
             "org.matrix.msc2762.send.event:org.matrix.msc4310.rtc.decline",
             "org.matrix.msc2762.send.event:m.rtc.decline",
@@ -593,6 +594,84 @@ describe("ElementWidgetDriver", () => {
         });
     });
 
+    describe("sendStickyEvent", () => {
+        let driver: WidgetDriver;
+        const roomId = "!this-room-id";
+
+        beforeEach(() => {
+            driver = mkDefaultDriver();
+        });
+
+        it("sends sticky message events", async () => {
+            client._unstable_sendStickyEvent.mockResolvedValue({
+                event_id: "id",
+            });
+
+            await expect(driver.sendStickyEvent(2000, EventType.RoomMessage, {})).resolves.toEqual({
+                roomId,
+                eventId: "id",
+            });
+
+            expect(client._unstable_sendStickyEvent).toHaveBeenCalledWith(
+                roomId,
+                2000,
+                null,
+                EventType.RoomMessage,
+                {},
+            );
+        });
+    });
+
+    describe("sendDelayedStickyEvent", () => {
+        let driver: WidgetDriver;
+        const roomId = "!this-room-id";
+
+        beforeEach(() => {
+            driver = mkDefaultDriver();
+        });
+
+        it("sends delayed sticky message events", async () => {
+            client._unstable_sendStickyDelayedEvent.mockResolvedValue({
+                delay_id: "id",
+            });
+
+            await expect(driver.sendDelayedStickyEvent(1000, null, 2000, EventType.RoomMessage, {})).resolves.toEqual({
+                roomId,
+                delayId: "id",
+            });
+
+            expect(client._unstable_sendStickyDelayedEvent).toHaveBeenCalledWith(
+                roomId,
+                2000,
+                { delay: 1000 },
+                null,
+                EventType.RoomMessage,
+                {},
+            );
+        });
+        it("sends child action delayed sticky message events", async () => {
+            client._unstable_sendStickyDelayedEvent.mockResolvedValue({
+                delay_id: "id-child",
+            });
+
+            await expect(
+                driver.sendDelayedStickyEvent(null, "id-parent", 2000, EventType.RoomMessage, {}),
+            ).resolves.toEqual({
+                roomId,
+                delayId: "id-child",
+            });
+
+            expect(client._unstable_sendStickyDelayedEvent).toHaveBeenCalledWith(
+                roomId,
+                2000,
+                { parent_delay_id: "id-parent" },
+                null,
+                EventType.RoomMessage,
+                {},
+            );
+        });
+    });
+
     describe("If the feature_dynamic_room_predecessors feature is not enabled", () => {
         beforeEach(() => {
             jest.spyOn(SettingsStore, "getValue").mockReturnValue(false);
diff --git a/yarn.lock b/yarn.lock
index 20ad046f5d..3d7c3ec0e0 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1577,17 +1577,8 @@
     yaml "^2.7.0"
 
 "@element-hq/web-shared-components@link:packages/shared-components":
-  version "0.0.0-test.12"
-  dependencies:
-    "@element-hq/element-web-module-api" "^1.8.0"
-    "@vector-im/compound-design-tokens" "^6.3.0"
-    classnames "^2.5.1"
-    counterpart "^0.18.6"
-    lodash "^4.17.21"
-    matrix-web-i18n "^3.4.0"
-    patch-package "^8.0.1"
-    react-merge-refs "^3.0.2"
-    temporal-polyfill "^0.3.0"
+  version "0.0.0"
+  uid ""
 
 "@emnapi/core@^1.4.3":
   version "1.7.0"
@@ -4223,6 +4214,7 @@
 
 "@vector-im/matrix-wysiwyg-wasm@link:../../../.cache/yarn/v6/npm-@vector-im-matrix-wysiwyg-2.40.0-53c9ca5ea907d91e4515da64f20a82e5586b882c-integrity/node_modules/bindings/wysiwyg-wasm":
   version "0.0.0"
+  uid ""
 
 "@vector-im/matrix-wysiwyg@2.40.0":
   version "2.40.0"
@@ -9693,7 +9685,7 @@ matrix-web-i18n@^3.2.1, matrix-web-i18n@^3.4.0:
     minimist "^1.2.8"
     walk "^2.3.15"
 
-matrix-widget-api@^1.14.0:
+matrix-widget-api@^1.10.0, matrix-widget-api@^1.15.0:
   version "1.15.0"
   resolved "https://registry.yarnpkg.com/matrix-widget-api/-/matrix-widget-api-1.15.0.tgz#a508f72a5993a95382bdf890bd9e54525295b321"
   integrity sha512-Yu9rX9wyF3A1sqviKgiYHz8aGgL3HhJe9OXKi/lccr1eZnNb6y+ELdbshTjs+VLKM4rkTWt6CE3THsw3f/CZhg==