Voice

"use client";import { CopilotKit } from "@copilotkit/react-core/v2";import { VoiceChat } from "./voice-chat";export default function VoiceDemoPage() {  return (    <CopilotKit      runtimeUrl="/api/copilotkit-voice"      agent="voice-demo"      useSingleEndpoint={false}      // The dev-only `<cpk-web-inspector>` overlay (auto-enabled on      // localhost via shouldShowDevConsole) intercepts pointer events      // on top of the voice sample-audio button, so dev/D5 probe runs      // can't click it through Playwright. Production isn't localhost      // so the inspector never mounts there — voice is D5 in prod and      // D4 locally for this reason alone. Disable explicitly here so      // the demo behaves the same in both environments.      enableInspector={false}    >      <VoiceChat />    </CopilotKit>  );}

You have a working chat surface and you want users to be able to speak instead of type. By the end of this guide, the chat composer will sprout a mic button, recorded audio will be transcribed by the runtime, and the transcript will auto-send to the agent like any other message.

When to use this#

Hands-free or accessibility flows where typing isn't the right input modality.
Mobile or kiosk surfaces where a long voice query is faster than thumb-typing.
Demo and test loops where you want canned audio to drive the chat without a microphone.

If you only need file uploads (audio, images, video, documents), use Multimodal Attachments instead. Voice is specifically about live transcription of recorded speech into chat input.

Frontend#

<CopilotChat /> from @copilotkit/react-core/v2 renders the mic button automatically when the runtime advertises audioFileTranscriptionEnabled: true on its /info endpoint. There's nothing to wire up on the chat surface itself:

page.tsx

import { CopilotKit } from "@copilotkit/react-core/v2";import { VoiceChat } from "./voice-chat";export default function VoiceDemoPage() {  return (    <CopilotKit      runtimeUrl="/api/copilotkit-voice"      agent="voice-demo"      useSingleEndpoint={false}      // The dev-only `<cpk-web-inspector>` overlay (auto-enabled on      // localhost via shouldShowDevConsole) intercepts pointer events      // on top of the voice sample-audio button, so dev/D5 probe runs      // can't click it through Playwright. Production isn't localhost      // so the inspector never mounts there — voice is D5 in prod and      // D4 locally for this reason alone. Disable explicitly here so      // the demo behaves the same in both environments.      enableInspector={false}    >      <VoiceChat />    </CopilotKit>  );}

The runtimeUrl="/api/copilotkit-voice" points the browser to your Next.js API route. When the user clicks the mic, the chat captures audio, POSTs it to that runtime route's /transcribe endpoint, drops the resulting transcript into the composer, and submits.

Driving the demo without a mic#

For Playwright runs, screenshots, or any flow where prompting for mic permissions is awkward, ship a button that emits a canned sample phrase through an onTranscribed callback, bypassing the transcription endpoint entirely:

sample-audio-button.tsx

export function SampleAudioButton({  onTranscribed,  sampleText,}: SampleAudioButtonProps) {  return (    <button      type="button"      data-testid="voice-sample-audio-button"      onClick={() => onTranscribed(sampleText)}      title={`Inserts: "${sampleText}"`}      className="inline-flex w-fit items-center gap-2 rounded-md border border-black/10 bg-white px-3 py-1.5 text-xs font-medium hover:bg-black/5 dark:border-white/10 dark:bg-black/30 dark:hover:bg-white/10"    >      <span aria-hidden>🎙</span>      <span>Try a sample audio</span>    </button>  );}

The parent chat component can then drop that text into the composer's textarea (matched via data-testid="copilot-chat-textarea") using the native value setter and a synthetic input event so React's managed state updates correctly.

Backend#

Next.js API route#

Create a dedicated API route at app/api/copilotkit-voice/[[...slug]]/route.ts. The [[...slug]] catch-all pattern lets the V2 runtime handle its internal URL routing (/info, /agent/:id/run, /transcribe, etc.) under the /api/copilotkit-voice base path.

Wire up the V2 runtime with a TranscriptionService. The V1 wrapper drops the transcriptionService option, so use createCopilotRuntimeHandler from @copilotkit/runtime/v2 directly:

route.ts

import type { NextRequest } from "next/server";import {  CopilotRuntime,  TranscriptionService,  createCopilotRuntimeHandler,} from "@copilotkit/runtime/v2";import type {  CopilotRuntimeOptions,  TranscribeFileOptions,} from "@copilotkit/runtime/v2";import { createClaudeHttpAgent } from "@/app/api/_shared/claude-http-agent";import { TranscriptionServiceOpenAI } from "@copilotkit/voice";import OpenAI from "openai";const AGENT_URL = process.env.AGENT_URL || "http://localhost:8000";const voiceDemoAgent = createClaudeHttpAgent(`${AGENT_URL}/`);type StaticRuntimeAgents = Awaited<  Exclude<CopilotRuntimeOptions["agents"], (...args: never[]) => unknown>>;type RuntimeAgent = StaticRuntimeAgents[keyof StaticRuntimeAgents];// CopilotRuntime and the app can resolve AbstractAgent from different// @ag-ui/client package instances during local development. AbstractAgent has// private fields, so TypeScript treats otherwise-compatible HttpAgent values// nominally. Keep that bridge at the runtime boundary.const voiceDemoAgents: Record<string, RuntimeAgent> = {  "voice-demo": voiceDemoAgent as unknown as RuntimeAgent,  default: voiceDemoAgent as unknown as RuntimeAgent,};class GuardedOpenAITranscriptionService extends TranscriptionService {  private delegate: TranscriptionServiceOpenAI | null;  constructor() {    super();    const apiKey = process.env.OPENAI_API_KEY;    this.delegate = apiKey      ? new TranscriptionServiceOpenAI({ openai: new OpenAI({ apiKey }) })      : null;  }  async transcribeFile(options: TranscribeFileOptions): Promise<string> {    if (!this.delegate) {      throw new Error(        "OPENAI_API_KEY not configured for this deployment (api key missing). " +          "Set OPENAI_API_KEY to enable voice transcription.",      );    }    return this.delegate.transcribeFile(options);  }}let cachedHandler: ((req: Request) => Promise<Response>) | null = null;function getHandler(): (req: Request) => Promise<Response> {  if (cachedHandler) return cachedHandler;  const runtime = new CopilotRuntime({    agents: voiceDemoAgents,    transcriptionService: new GuardedOpenAITranscriptionService(),  });  cachedHandler = createCopilotRuntimeHandler({    runtime,    basePath: "/api/copilotkit-voice",  });  return cachedHandler;}export const POST = (req: NextRequest) => getHandler()(req);export const GET = (req: NextRequest) => getHandler()(req);export const PUT = (req: NextRequest) => getHandler()(req);export const DELETE = (req: NextRequest) => getHandler()(req);

The basePath: "/api/copilotkit-voice" in createCopilotRuntimeHandler must match the API route's directory path. With transcriptionService set, the runtime advertises audioFileTranscriptionEnabled: true on /info (which is what tells the chat to render the mic button) and routes POST /transcribe to the service.

Without a service, `/transcribe` answers 503

A runtime with no transcriptionService still serves the route, and answers every request 503 with { "error": "service_not_configured" }. The mic button never appears, so the symptom is a chat with no voice input rather than a visible server error — check /info for audioFileTranscriptionEnabled when voice silently doesn't show up.

Calling `/transcribe` yourself

The chat handles this for you; these are the rules if you post to the route directly. As multipart, the audio field must be named audio — any other name reads as absent and the route answers invalid_request. As JSON, mimeType is required alongside the base64 audio, and a payload without it is rejected the same way.

Custom transcription backends#

TranscriptionService from @copilotkit/runtime/v2 is an abstract class. Subclass it to plug in any transcription provider — Whisper, AssemblyAI, Deepgram, your own model. The library ships TranscriptionServiceOpenAI as the canonical reference implementation.

Return a string, and let provider errors through

transcribe returns the transcript as a string — the handler wraps it into { transcription } itself, so returning a richer object is a type error.

Let the provider's own errors propagate unchanged. The runtime classifies failures by reading the error text for markers like rate, 429, auth and too long, so a provider message such as OpenAI returned 429 rate limited maps to the right error code on its own. Replacing it with your own wording bypasses that and everything lands as a generic provider error.

A useful pattern is constructing the service only when its dedicated credential is configured. Without it, omit transcriptionService; the runtime reports the capability as disabled, hides the mic, and returns the documented 503 if /transcribe is called directly: