diff --git a/packages/platform/CHANGELOG.md b/packages/platform/CHANGELOG.md
index 67590b32..da668095 100644
--- a/packages/platform/CHANGELOG.md
+++ b/packages/platform/CHANGELOG.md
@@ -2,8 +2,8 @@
 
 ## 0.2.0
 
-**Breaking.** The client, its options and the event type names change. Runtime delivery of events
-is unchanged.
+**Breaking.** The client, its options and the event type names change, and events the SDK doesn't
+know now reach `onEvent`.
 
 ### Client and session
 
@@ -61,6 +61,9 @@ names.
   `WriteFileCall`. Check `name` to narrow it to that tool's `arguments` and `display`.
   `ToolArguments` and `ToolDisplay` are removed.
 - `BranchScoped` is removed. Each payload that belongs to a branch has its own `branch_id`.
+- `PlatformEvent` gains a member for events newer than the SDK: `{ type: "unknown", name, appId,
+  data }`, where `data` is `Record<string, unknown>`. Before, the SDK dropped them. A `switch` on
+  `event.type` that must cover every case needs a `case "unknown"`.
 - New: `SessionErrorCode` and `AppErrorCode` split `PlatformSocketErrorCode`, and every schema in
   the protocol is exported, with `ServerEventMap` and `ClientMessageMap`.
 
diff --git a/packages/platform/README.md b/packages/platform/README.md
index a39273ab..e311d789 100644
--- a/packages/platform/README.md
+++ b/packages/platform/README.md
@@ -115,7 +115,9 @@ their exceptions are isolated so they cannot interrupt another app's delivery.
 event is `{room, data}`; the SDK routes by `room` and validates the envelope, while
 payload schemas and private-field filtering are the server's. Omitted keys mean
 unchanged and explicit null clears. Events carrying `branch_id` belong to that branch;
-null or absent is main. Unknown event names are not forwarded. `PlatformSnapshot` is
+null or absent is main. An event name the SDK doesn't know is forwarded as
+`{type: "unknown", name, appId, data}` with only the envelope validated, so a new event reaches
+partners when the service deploys it; new `room.*` notices are dropped. `PlatformSnapshot` is
 the service's `Snapshot` plus the app's `room`. Structural filtering does not promise
 redaction of generated prose or user content.
 
diff --git a/packages/platform/src/modules/builder-protocol.ts b/packages/platform/src/modules/builder-protocol.ts
index 91f8f219..7d979923 100644
--- a/packages/platform/src/modules/builder-protocol.ts
+++ b/packages/platform/src/modules/builder-protocol.ts
@@ -8,6 +8,9 @@ const sessionEvents: readonly string[] = ["app.snapshot", "session.ended"];
 export const eventNames = serverEventNames.filter(
   (name): name is keyof PlatformEventMap & typeof name => !sessionEvents.includes(name) && !name.startsWith("room."),
 );
+const knownNames: readonly string[] = serverEventNames;
+/** A name newer than this SDK's protocol, delivered to `onEvent` as `unknown`. New `room.*` notices have no error code, so they are dropped. */
+export const isUnknownEvent = (name: string) => !knownNames.includes(name) && !name.startsWith("room.");
 /** Notices that name an app room, by the error code each one reports. A new notice fails to compile until it has one. */
 export const roomNotices = {
   "room.access_denied": "access_denied",
@@ -31,8 +34,9 @@ export function appFromRoom(value: unknown): string | undefined {
   return typeof value === "string" && /^\/apps\/[a-f0-9]{24}$/.test(value) ? value.slice(6) : undefined;
 }
 /** Every event is `{room, data}`; payload schemas are the service's, so only the envelope is validated. */
-export function decode(type: keyof PlatformEventMap, appId: string, raw: unknown): PlatformEvent {
-  return { type, appId, data: object(object(raw).data) } as PlatformEvent;
+export function decode(name: string, appId: string, raw: unknown): PlatformEvent {
+  const data = object(object(raw).data);
+  return (knownNames.includes(name) ? { type: name, appId, data } : { type: "unknown", name, appId, data }) as PlatformEvent;
 }
 export function decodeSnapshot(raw: unknown): PlatformSnapshot {
   const frame = object(raw);
diff --git a/packages/platform/src/modules/builder-socket.ts b/packages/platform/src/modules/builder-socket.ts
index 542fb877..08bcf408 100644
--- a/packages/platform/src/modules/builder-socket.ts
+++ b/packages/platform/src/modules/builder-socket.ts
@@ -1,6 +1,6 @@
 import { io, type Socket } from "socket.io-client";
 import { PlatformSocketError } from "../errors.js";
-import { appFromRoom, appPattern, decode, decodeSession, decodeSnapshot, eventNames, object, roomFor, roomNotices, sessionEndings } from "./builder-protocol.js";
+import { appFromRoom, appPattern, decode, decodeSession, decodeSnapshot, eventNames, isUnknownEvent, object, roomFor, roomNotices, sessionEndings } from "./builder-protocol.js";
 import { notify, Subscription } from "./builder-subscription.js";
 import type { BuilderInitOptions, BuilderSession, PlatformSubscription, SocketSession, SubscriptionOptions } from "./builder.types.js";
 
@@ -113,23 +113,27 @@ export class BuilderSocket implements BuilderSession {
     });
     socket.on("session.ended", (raw: unknown) => this.sessionEnded(raw));
     for (const [name, code] of Object.entries(roomNotices)) socket.on(name, (raw: unknown) => this.roomNotice(code, raw));
-    for (const type of eventNames) socket.on(type, (raw: unknown) => {
-      try {
-        const appId = appFromRoom(object(raw).room);
-        if (!appId) throw new Error("Invalid app");
-        const event = decode(type, appId, raw);
-        const subscription = this.subscriptions.get(appId);
-        subscription?.event(event);
-        // The server does not resend a snapshot after a rewrite of main: rejoining asks for one.
-        if (subscription && event.type === "conversation.changed" && event.data.branch_id == null) this.join(subscription);
-      } catch { this.protocolError(raw); }
-    });
+    for (const name of eventNames) socket.on(name, (raw: unknown) => this.appEvent(name, raw));
+    socket.onAny((name: string, raw: unknown) => { if (isUnknownEvent(name)) this.appEvent(name, raw); });
     socket.connect();
   }
 
+  private appEvent(name: string, raw: unknown): void {
+    try {
+      const appId = appFromRoom(object(raw).room);
+      if (!appId) throw new Error("Invalid app");
+      const event = decode(name, appId, raw);
+      const subscription = this.subscriptions.get(appId);
+      subscription?.event(event);
+      // The server does not resend a snapshot after a rewrite of main: rejoining asks for one.
+      if (subscription && event.type === "conversation.changed" && event.data.branch_id == null) this.join(subscription);
+    } catch { this.protocolError(raw); }
+  }
+
   private discard(): void {
     if (!this.socket) return;
     this.socket.removeAllListeners();
+    this.socket.offAny();
     this.socket.io.removeAllListeners();
     this.socket.disconnect();
   }
diff --git a/packages/platform/src/modules/builder.events.types.ts b/packages/platform/src/modules/builder.events.types.ts
index dfc9dc30..60294450 100644
--- a/packages/platform/src/modules/builder.events.types.ts
+++ b/packages/platform/src/modules/builder.events.types.ts
@@ -18,6 +18,10 @@ export type PlatformEventMap = {
  * is unchanged, and an explicit `null` clears it. For every event and its payload, see
  * [Socket messages](/developers/references/apps-api/sections/socket-messages).
  *
+ * An event added to the service after this version of the SDK arrives with `type: "unknown"`, its
+ * name in `name` and an unchecked `data`, so check a field before using it. After you upgrade, it
+ * arrives under its own `type`.
+ *
  * @example
  * ```typescript
  * // Narrow an event by type
@@ -26,6 +30,9 @@ export type PlatformEventMap = {
  *     const { message } = event.data;
  *     console.log(`Message ${message.id} changed`);
  *   }
+ *   if (event.type === "unknown" && event.name === "app.renamed" && typeof event.data.name === "string") {
+ *     console.log(`App renamed to ${event.data.name}`);
+ *   }
  * }
  * ```
  */
@@ -38,7 +45,16 @@ export type PlatformEvent = {
     /** Event payload. */
     data: PlatformEventMap[K];
   };
-}[keyof PlatformEventMap];
+}[keyof PlatformEventMap] | {
+  /** An event this version of the SDK doesn't know. */
+  type: "unknown";
+  /** The event's name on the socket. */
+  name: string;
+  /** ID of the app the event belongs to. */
+  appId: string;
+  /** Event payload, not checked by the SDK. */
+  data: Record<string, unknown>;
+};
 
 /**
  * An app's current state.
diff --git a/packages/platform/src/modules/builder.types.ts b/packages/platform/src/modules/builder.types.ts
index 7f55d68f..064ab695 100644
--- a/packages/platform/src/modules/builder.types.ts
+++ b/packages/platform/src/modules/builder.types.ts
@@ -168,7 +168,8 @@ export interface SubscriptionOptions {
   /**
    * Called with each live event, a [`PlatformEvent`](#platformevent). Events for an app arrive one at a time, in order. If the callback
    * throws or rejects, the subscription ends with `handler_failed`. New event types can be added at
-   * any time, so ignore types you don't handle. For every event and its payload,
+   * any time, so ignore types you don't handle. An event newer than this SDK arrives with
+   * `type: "unknown"` and its name in `name`. For every event and its payload,
    * see [Socket messages](/developers/references/apps-api/sections/socket-messages).
    */
   onEvent: (event: PlatformEvent) => void | Promise<void>;
diff --git a/packages/platform/tests/types/client.types.ts b/packages/platform/tests/types/client.types.ts
index 6750e820..a16746b8 100644
--- a/packages/platform/tests/types/client.types.ts
+++ b/packages/platform/tests/types/client.types.ts
@@ -40,6 +40,13 @@ const subscription = builder.subscribe("a".repeat(24), {
       const status: "pending" | "completed" | "failed" | null | undefined = event.data.status;
       void status;
     }
+    if (event.type === "unknown") {
+      const name: string = event.name;
+      // @ts-expect-error An unknown event's payload is unchecked.
+      const title: string = event.data.title;
+      if (typeof event.data.title === "string") void event.data.title.length;
+      void name; void title;
+    }
     // @ts-expect-error Payload must be narrowed by event.type.
     void event.data.items;
     // @ts-expect-error There is no replay cursor.
diff --git a/packages/platform/tests/unit/client.test.ts b/packages/platform/tests/unit/client.test.ts
index 0f4ad838..ce75c2e3 100644
--- a/packages/platform/tests/unit/client.test.ts
+++ b/packages/platform/tests/unit/client.test.ts
@@ -7,7 +7,8 @@ const fake = vi.hoisted(() => {
   const socket = {
     connected: false,
     on: vi.fn((name, handler) => { handlers[name] = handler; }),
-    emit: vi.fn(), connect: vi.fn(), disconnect: vi.fn(), removeAllListeners: vi.fn(),
+    onAny: vi.fn(handler => { handlers["*"] = handler; }),
+    emit: vi.fn(), connect: vi.fn(), disconnect: vi.fn(), removeAllListeners: vi.fn(), offAny: vi.fn(),
     io: { on: vi.fn((name, handler) => { managerHandlers[name] = handler; }), removeAllListeners: vi.fn() },
   };
   return { handlers, managerHandlers, socket, io: vi.fn(() => socket) };
@@ -353,6 +354,28 @@ describe("platform client", () => {
     expect(onError.mock.calls[0][0].code).toBe("protocol_error");
   });
 
+  test("forwards an event the SDK doesn't know to its app only", async () => {
+    const { client } = setup(); const onEvent = vi.fn(), otherEvent = vi.fn();
+    client.subscribe(app, { onSnapshot: vi.fn(), onEvent, onError: vi.fn() });
+    client.subscribe(other, { onSnapshot: vi.fn(), onEvent: otherEvent, onError: vi.fn() });
+    await connected(client);
+    for (const name of ["app.renamed", "message.updated", "app.snapshot", "session.ended", "room.access_denied", "room.new_notice"]) {
+      fake.handlers["*"](name, { room, data: { name: "Shop" } });
+    }
+    await settle();
+    expect(onEvent.mock.calls).toEqual([[{ type: "unknown", name: "app.renamed", appId: app, data: { name: "Shop" } }]]);
+    expect(otherEvent).not.toHaveBeenCalled();
+  });
+
+  test("a malformed unknown event fails only its app", async () => {
+    const { client } = setup(); const onError = vi.fn();
+    const sub = client.subscribe(app, { onSnapshot: vi.fn(), onEvent: vi.fn(), onError });
+    const second = client.subscribe(other, { onSnapshot: vi.fn(), onEvent: vi.fn(), onError: vi.fn() }); await connected(client);
+    fake.handlers["*"]("app.renamed", { room, data: [] });
+    expect(sub.active).toBe(false); expect(second.active).toBe(true);
+    expect(onError.mock.calls[0][0].code).toBe("protocol_error");
+  });
+
   test("bounded pending delivery overflows explicitly", async () => {
     const { client } = setup(); const onError = vi.fn();
     const sub = client.subscribe(app, { onSnapshot: vi.fn(), onEvent: () => new Promise(() => {}), onError });
@@ -368,7 +391,7 @@ describe("platform client", () => {
     expect(joins()).toEqual([["join", room], ["join", room]]);
     client.close(); client.close(); expect(fake.socket.disconnect).toHaveBeenCalledOnce();
     await expect(client.connect()).rejects.toMatchObject({ code: "client_closed" });
-    expect(fake.socket.removeAllListeners).toHaveBeenCalledOnce();
+    expect(fake.socket.removeAllListeners).toHaveBeenCalledOnce(); expect(fake.socket.offAny).toHaveBeenCalledOnce();
   });
 
   test("validates app IDs, duplicate subscriptions and limits", () => {