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xai/grok-voice

Build real-time voice applications powered by Grok. Send recorded audio and get a voice and text response.
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Table of contents

About

Generate the Grok voice agent's spoken reply to an uploaded audio file.

One-shot alternative to /realtime: the app connects to xAI, configures the session (prompt / voice / tools), streams the whole input recording, requests a single response, and returns the agent's reply as a WAV file plus its transcript.

1. Calling the API#

Install the client#

The client provides a convenient way to interact with the model API.

npm install --save @fal-ai/client

Setup your API Key#

Set FAL_KEY as an environment variable in your runtime.

export FAL_KEY="YOUR_API_KEY"

Submit a request#

The client API handles the API submit protocol. It will handle the request status updates and return the result when the request is completed.

import { fal } from "@fal-ai/client";

const result = await fal.subscribe("xai/grok-voice", {
  input: {
    audio_url: "https://v3b.fal.media/files/b/0a8dd5a2/hS140ygvRuxn-eY_qPhlv_assets_test_input_service.wav"
  },
  logs: true,
  onQueueUpdate: (update) => {
    if (update.status === "IN_PROGRESS") {
      update.logs.map((log) => log.message).forEach(console.log);
    }
  },
});
console.log(result.data);
console.log(result.requestId);

2. Authentication#

The API uses an API Key for authentication. It is recommended you set the FAL_KEY environment variable in your runtime when possible.

API Key#

In an environment where you cannot set environment variables, you can configure the API key manually on the client.
import { fal } from "@fal-ai/client";

fal.config({
  credentials: "YOUR_FAL_KEY"
});

3. Queue#

Submit a request#

The client API provides a convenient way to submit requests to the model.

import { fal } from "@fal-ai/client";

const { request_id } = await fal.queue.submit("xai/grok-voice", {
  input: {
    audio_url: "https://v3b.fal.media/files/b/0a8dd5a2/hS140ygvRuxn-eY_qPhlv_assets_test_input_service.wav"
  },
  webhookUrl: "https://optional.webhook.url/for/results",
});

Fetch request status#

You can fetch the status of a request to check if it is completed or still in progress.

import { fal } from "@fal-ai/client";

const status = await fal.queue.status("xai/grok-voice", {
  requestId: "764cabcf-b745-4b3e-ae38-1200304cf45b",
  logs: true,
});

Get the result#

Once the request is completed, you can fetch the result. See the Output Schema for the expected result format.

import { fal } from "@fal-ai/client";

const result = await fal.queue.result("xai/grok-voice", {
  requestId: "764cabcf-b745-4b3e-ae38-1200304cf45b"
});
console.log(result.data);
console.log(result.requestId);

4. Files#

Some attributes in the API accept file URLs as input. Whenever that's the case you can pass your own URL or a Base64 data URI.

Data URI (base64)#

You can pass a Base64 data URI as a file input. The API will handle the file decoding for you. Keep in mind that for large files, this alternative although convenient can impact the request performance.

Hosted files (URL)#

You can also pass your own URLs as long as they are publicly accessible. Be aware that some hosts might block cross-site requests, rate-limit, or consider the request as a bot.

Uploading files#

We provide a convenient file storage that allows you to upload files and use them in your requests. You can upload files using the client API and use the returned URL in your requests.

import { fal } from "@fal-ai/client";

const file = new File(["Hello, World!"], "hello.txt", { type: "text/plain" });
const url = await fal.storage.upload(file);

Read more about file handling in our file upload guide.

5. Schema#

Input#

audio_url string* required

URL of the audio containing the user's speech. The Grok agent listens to it and replies with speech. Most common audio formats are supported; the audio is converted to 16-bit 24 kHz mono PCM before being sent to Grok. Maximum duration 10 minutes, maximum file size 50 MB.

prompt string

Optional system instructions describing the agent's persona and conversation context. Uses Grok's default persona when omitted.

voice Enum

Built-in xAI voice for the agent's reply. Uses Grok's default voice when omitted.

Possible enum values: carina, zagan, helix, orion, luna, iris, altair, zenith, perseus, helios, lux, kepler, rigel, cosmo, celeste, ursa, sirius, lumen, castor, naksh, atlas, aurora, liora, ara, eve, leo, rex, sal

tools GrokToolsConfiguration

Server-side tools available to the agent. Web, X, and remote MCP tools are supported; every tool is disabled by default. file_search/collections are unsupported by the typed configuration due to ZDR.

{
  "audio_url": "https://v3b.fal.media/files/b/0a8dd5a2/hS140ygvRuxn-eY_qPhlv_assets_test_input_service.wav",
  "prompt": "You are a friendly assistant. Answer briefly and concretely."
}

Output#

audio File* required

The Grok agent's spoken response (WAV, 24 kHz mono).

text string

Transcript of the agent's spoken response, when Grok provides one (empty string otherwise). Default value: ""

duration float* required

Duration of the generated audio in seconds.

{
  "audio": {
    "url": "",
    "content_type": "image/png",
    "file_name": "z9RV14K95DvU.png",
    "file_size": 4404019
  },
  "duration": 7.4
}

Other types#

GrokSearchLocation#

timezone string

IANA timezone name, for example America/New_York. Default value: "null"

city string

City used to localize web-search results. Default value: "null"

country string

Country used to localize web-search results. Default value: "null"

region string

Region used to localize web-search results. Default value: "null"

GrokRemoteMCPTool#

authorization string

Sensitive authorization value forwarded only to xAI. Default value: "null"

server_label string* required

Label xAI uses to identify and prefix this server's tools.

server_description string

Description of the capabilities exposed by this server. Default value: "null"

server_url string* required

Caller-selected HTTP(S) MCP endpoint. xAI makes the remote connection and supports Streaming HTTP/SSE transports. Use at your own risk; fal does not connect to or SSRF-fetch this URL.

allowed_tools list<string>

Optional allow-list of tool names exposed from this server.

headers object

Sensitive MCP request headers forwarded only to xAI.

enabled boolean

False omits this server. Default value: true

File#

url string* required

The URL where the file can be downloaded from.

content_type string

The mime type of the file.

file_name string

The name of the file. It will be auto-generated if not provided.

file_size integer

The size of the file in bytes.

GrokTurnDetectionConfiguration#

silence_duration_ms integer

Silence duration that ends a detected turn, in milliseconds.

idle_timeout_ms integer

Idle time after an assistant response before xAI starts a proactive turn, in milliseconds.

threshold float

VAD activation threshold; higher values require louder audio.

prefix_padding_ms integer

Audio retained before detected speech, in milliseconds.

GrokXSearchTool#

excluded_x_handles list<string>

Exclude posts from at most 20 X handles.

enable_image_understanding boolean

Allow the agent to inspect images found on X.

enable_video_understanding boolean

Allow the agent to inspect videos found on X.

allowed_x_handles list<string>

Restrict results to posts from at most 20 X handles.

to_date string

Latest post date, as ISO YYYY-MM-DD. Default value: "null"

from_date string

Earliest post date, as ISO YYYY-MM-DD. Default value: "null"

enabled boolean

Whether to include x_search in session.tools. Disabled by default; set true to let the agent search X posts.

GrokToolsConfiguration#

x_search GrokXSearchTool

xAI-managed X search; off unless enabled is set true.

mcp_servers list<GrokRemoteMCPTool>

Remote MCP servers that xAI connects to and executes.

web_search GrokWebSearchTool

xAI-managed web search; off unless enabled is set true.

GrokWebSearchTool#

excluded_domains list<string>

Exclude results from at most five domains, without protocol or path.

allowed_domains list<string>

Restrict results to at most five domains, without protocol or path.

location GrokSearchLocation

Optional location used to localize search results.

enable_image_understanding boolean

Allow the agent to inspect images found during web search.

enabled boolean

Whether to include web_search in session.tools. Disabled by default; set true to let the agent search the web.

GrokRealtimeEvent#

prompt string

System instructions describing the agent's persona and conversation context. Uses Grok's default persona when omitted. Default value: "null"

voice Enum

Built-in xAI voice for the agent's speech. Uses Grok's default voice when omitted.

Possible enum values: carina, zagan, helix, orion, luna, iris, altair, zenith, perseus, helios, lux, kepler, rigel, cosmo, celeste, ursa, sirius, lumen, castor, naksh, atlas, aurora, liora, ara, eve, leo, rex, sal

turn_detection GrokTurnDetectionConfiguration

Automatic turn detection: any configured object (even empty) lets the agent detect when you stop speaking and reply on its own. Set null for manual turns; omit to keep the session default.

type string* required

xAI realtime event type (e.g. 'session.update', 'input_audio_buffer.append', 'response.create', 'response.output_audio.delta'). Events are relayed verbatim in both directions.

tools GrokToolsConfiguration

Server-side tools available to the agent. Web, X, and remote MCP tools are supported; every tool is disabled by default. An explicitly supplied object always reaches the session, so previously enabled tools can be cleared.

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