diff --git a/src/app/api/runtimes/[id]/talk/realtime/relay/route.test.ts b/src/app/api/runtimes/[id]/talk/realtime/relay/route.test.ts
index e4384a7e..79b89335 100644
--- a/src/app/api/runtimes/[id]/talk/realtime/relay/route.test.ts
+++ b/src/app/api/runtimes/[id]/talk/realtime/relay/route.test.ts
@@ -83,6 +83,28 @@ describe("POST /api/runtimes/[id]/talk/realtime/relay", () => {
     });
   });
 
+  it("proxies realtime output cancellation through an accessible runtime", async () => {
+    const realtimeRelayCancelOutput = vi.fn().mockResolvedValue({ ok: true });
+    mockRuntimeRows.push({ id: "rt_1", ownerUserId: "user_1" });
+    mockGetGatewayClientForRuntime.mockResolvedValue({ realtimeRelayCancelOutput });
+
+    const response = await POST(
+      new Request("http://localhost/api/runtimes/rt_1/talk/realtime/relay", {
+        method: "POST",
+        body: JSON.stringify({
+          action: "cancelOutput",
+          relaySessionId: "relay_1",
+          reason: "barge-in",
+        }),
+      }),
+      { params: Promise.resolve({ id: "rt_1" }) },
+    );
+
+    expect(response.status).toBe(200);
+    await expect(response.json()).resolves.toEqual({ result: { ok: true } });
+    expect(realtimeRelayCancelOutput).toHaveBeenCalledWith("relay_1", "barge-in");
+  });
+
   it("rejects invalid relay actions before calling the gateway", async () => {
     mockRuntimeRows.push({ id: "rt_1", ownerUserId: "user_1" });
 
diff --git a/src/app/api/runtimes/[id]/talk/realtime/relay/route.ts b/src/app/api/runtimes/[id]/talk/realtime/relay/route.ts
index f96ba8c3..8293166b 100644
--- a/src/app/api/runtimes/[id]/talk/realtime/relay/route.ts
+++ b/src/app/api/runtimes/[id]/talk/realtime/relay/route.ts
@@ -7,7 +7,7 @@ import { getGatewayClientForRuntime } from "@/lib/gateway-chat-pool";
 
 export const dynamic = "force-dynamic";
 
-type RelayAction = "audio" | "mark" | "toolResult" | "stop";
+type RelayAction = "audio" | "cancelOutput" | "mark" | "toolResult" | "stop";
 
 export async function POST(
   request: Request,
@@ -53,6 +53,14 @@ export async function POST(
       return NextResponse.json({ result });
     }
 
+    if (action === "cancelOutput") {
+      const result = await client.realtimeRelayCancelOutput(
+        relaySessionId,
+        readOptionalString(body.reason),
+      );
+      return NextResponse.json({ result });
+    }
+
     if (action === "toolResult") {
       const callId = readRequiredString(body.callId, "callId");
       const result = await client.realtimeRelayToolResult({
@@ -88,6 +96,6 @@ function readOptionalString(value: unknown) {
 }
 
 function readRelayAction(value: unknown): RelayAction {
-  if (value === "audio" || value === "mark" || value === "toolResult" || value === "stop") return value;
-  throw new ValidationError("action must be audio, mark, toolResult, or stop");
+  if (value === "audio" || value === "cancelOutput" || value === "mark" || value === "toolResult" || value === "stop") return value;
+  throw new ValidationError("action must be audio, cancelOutput, mark, toolResult, or stop");
 }
diff --git a/src/lib/gateway-client-realtime.test.ts b/src/lib/gateway-client-realtime.test.ts
index e39ea9d5..b59f977f 100644
--- a/src/lib/gateway-client-realtime.test.ts
+++ b/src/lib/gateway-client-realtime.test.ts
@@ -76,4 +76,16 @@ describe("GatewayClient realtime Talk compatibility", () => {
 
     expect(rpc).not.toHaveBeenCalled();
   });
+
+  it("maps output cancellation onto the unified session API", async () => {
+    const client = new GatewayClient("ws://localhost:18789", null, device);
+    const rpc = vi.spyOn(client, "rpc").mockResolvedValue({ ok: true });
+
+    await expect(client.realtimeRelayCancelOutput("relay_1", "barge-in")).resolves.toEqual({ ok: true });
+
+    expect(rpc).toHaveBeenCalledWith("talk.session.cancelOutput", {
+      sessionId: "relay_1",
+      reason: "barge-in",
+    });
+  });
 });
diff --git a/src/lib/gateway-client.ts b/src/lib/gateway-client.ts
index c3c896d7..e8dfea8d 100644
--- a/src/lib/gateway-client.ts
+++ b/src/lib/gateway-client.ts
@@ -768,6 +768,18 @@ export class GatewayClient {
     return { ok: true };
   }
 
+  async realtimeRelayCancelOutput(relaySessionId: string, reason?: string): Promise<{ ok?: boolean }> {
+    try {
+      return await this.rpc<{ ok?: boolean }>("talk.session.cancelOutput", withoutUndefined({
+        sessionId: relaySessionId,
+        reason,
+      }));
+    } catch (err) {
+      if (!isLikelyMissingGatewayMethod(err)) throw err;
+      return { ok: true };
+    }
+  }
+
   async realtimeRelayToolResult(params: GatewayRealtimeRelayToolResultParams): Promise<{ ok?: boolean }> {
     try {
       return await this.rpc<{ ok?: boolean }>("talk.session.submitToolResult", withoutUndefined({
diff --git a/src/lib/realtime-voice-client.test.ts b/src/lib/realtime-voice-client.test.ts
index 00c54014..05c50e2d 100644
--- a/src/lib/realtime-voice-client.test.ts
+++ b/src/lib/realtime-voice-client.test.ts
@@ -1,5 +1,6 @@
 import { beforeEach, describe, expect, it, vi } from "vitest";
 import {
+  cancelRealtimeRelayOutput,
   openRealtimeRelayEvents,
   sendRealtimeRelayAudio,
   startRealtimeVoiceSession,
@@ -57,6 +58,25 @@ describe("realtime voice client helpers", () => {
     });
   });
 
+  it("sends output cancellation through the runtime relay route", async () => {
+    const fetchMock = vi.spyOn(globalThis, "fetch").mockResolvedValue({
+      ok: true,
+      json: () => Promise.resolve({ result: { ok: true } }),
+    } as Response);
+
+    await cancelRealtimeRelayOutput("rt_1", "relay_1", "barge-in");
+
+    expect(fetchMock).toHaveBeenCalledWith("/api/runtimes/rt_1/talk/realtime/relay", {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({
+        action: "cancelOutput",
+        relaySessionId: "relay_1",
+        reason: "barge-in",
+      }),
+    });
+  });
+
   it("opens relay events for the selected runtime and session", () => {
     const eventSourceMock = vi.fn();
     vi.stubGlobal("EventSource", eventSourceMock);
diff --git a/src/lib/realtime-voice-client.ts b/src/lib/realtime-voice-client.ts
index c1c6c475..d69989a7 100644
--- a/src/lib/realtime-voice-client.ts
+++ b/src/lib/realtime-voice-client.ts
@@ -75,6 +75,18 @@ export async function sendRealtimeRelayMark(runtimeId: string, relaySessionId: s
   });
 }
 
+export async function cancelRealtimeRelayOutput(
+  runtimeId: string,
+  relaySessionId: string,
+  reason = "barge-in",
+): Promise<void> {
+  await postRealtimeRelay(runtimeId, {
+    action: "cancelOutput",
+    relaySessionId,
+    reason,
+  });
+}
+
 export async function sendRealtimeRelayToolResult(
   runtimeId: string,
   relaySessionId: string,
diff --git a/src/lib/realtime-voice-gateway-relay.ts b/src/lib/realtime-voice-gateway-relay.ts
index 7fcc571a..56f798cf 100644
--- a/src/lib/realtime-voice-gateway-relay.ts
+++ b/src/lib/realtime-voice-gateway-relay.ts
@@ -1,4 +1,5 @@
 import {
+  cancelRealtimeRelayOutput,
   openRealtimeRelayEvents,
   sendRealtimeRelayAudio,
   sendRealtimeRelayMark,
@@ -10,6 +11,10 @@ import { base64ToBytes, bytesToBase64, floatToPcm16, pcm16ToFloat, rmsLevel } fr
 
 export type RealtimeVoiceStatus = "idle" | "listening" | "processing" | "speaking" | "error";
 
+const BARGE_IN_RMS_THRESHOLD = 0.02;
+const BARGE_IN_PEAK_THRESHOLD = 0.08;
+const BARGE_IN_FRAMES = 2;
+
 export interface RealtimeGatewayRelayCallbacks {
   onStatus?: (status: RealtimeVoiceStatus, message?: string) => void;
   onTranscript?: (event: { role: "user" | "assistant"; text: string; final: boolean }) => void;
@@ -50,6 +55,8 @@ export class RealtimeGatewayRelaySession {
   private readonly sources = new Set<AudioBufferSourceNode>();
   private playhead = 0;
   private closed = false;
+  private cancelRequestedForPlayback = false;
+  private speechFramesDuringPlayback = 0;
 
   constructor(
     private readonly runtimeId: string,
@@ -128,6 +135,7 @@ export class RealtimeGatewayRelaySession {
     }
     this.sources.clear();
     this.playhead = this.outputContext?.currentTime ?? 0;
+    this.speechFramesDuringPlayback = 0;
     this.callbacks.onSpeakingChange?.(false);
   }
 
@@ -141,6 +149,7 @@ export class RealtimeGatewayRelaySession {
       const input = event.inputBuffer.getChannelData(0);
       this.callbacks.onVoiceLevel?.(rmsLevel(input));
       const pcm = floatToPcm16(input);
+      if (this.detectBargeInSpeech(input)) this.cancelOutputForBargeIn();
       void sendRealtimeRelayAudio(this.runtimeId, {
         relaySessionId: this.session.relaySessionId,
         audioBase64: bytesToBase64(pcm),
@@ -162,7 +171,10 @@ export class RealtimeGatewayRelaySession {
         this.callbacks.onStatus?.("listening");
         return;
       case "audio":
-        if (event.audioBase64) this.playPcm16(event.audioBase64);
+        if (event.audioBase64) {
+          this.cancelRequestedForPlayback = false;
+          this.playPcm16(event.audioBase64);
+        }
         return;
       case "clear":
         this.stopOutput();
@@ -235,4 +247,39 @@ export class RealtimeGatewayRelaySession {
       name: event.name ?? null,
     }).catch(() => {});
   }
+
+  private cancelOutputForBargeIn(): void {
+    if (!this.session.relaySessionId || this.cancelRequestedForPlayback) return;
+    this.cancelRequestedForPlayback = true;
+    this.stopOutput();
+    this.callbacks.onStatus?.("listening", "Interrupted");
+    void cancelRealtimeRelayOutput(this.runtimeId, this.session.relaySessionId, "barge-in").catch((error) => {
+      const message = error instanceof Error ? error.message : String(error);
+      this.callbacks.onError?.(message);
+    });
+  }
+
+  private detectBargeInSpeech(input: Float32Array): boolean {
+    if (this.sources.size === 0 || this.cancelRequestedForPlayback || input.length === 0) {
+      this.speechFramesDuringPlayback = 0;
+      return false;
+    }
+
+    let peak = 0;
+    let sum = 0;
+    for (const sample of input) {
+      const abs = Math.abs(sample);
+      peak = Math.max(peak, abs);
+      sum += sample * sample;
+    }
+
+    const rms = Math.sqrt(sum / input.length);
+    if (rms >= BARGE_IN_RMS_THRESHOLD && peak >= BARGE_IN_PEAK_THRESHOLD) {
+      this.speechFramesDuringPlayback += 1;
+    } else {
+      this.speechFramesDuringPlayback = 0;
+    }
+
+    return this.speechFramesDuringPlayback >= BARGE_IN_FRAMES;
+  }
 }