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xAI (Grok)

The xai provider supports xAI's Grok models through an API interface compatible with OpenAI's format. The provider supports both text and vision capabilities depending on the model used.

Setup​

To use xAI's API, set the XAI_API_KEY environment variable or specify via apiKey in the configuration file.

export XAI_API_KEY=your_api_key_here

Supported Models​

The xAI provider includes support for the following model formats:

Grok 4.1 Fast Models​

  • xai:grok-4-1-fast-reasoning - Frontier model optimized for agentic tool calling with reasoning (2M context)
  • xai:grok-4-1-fast-non-reasoning - Fast variant for instant responses without reasoning (2M context)
  • xai:grok-4-1-fast - Alias for grok-4-1-fast-reasoning
  • xai:grok-4-1-fast-latest - Alias for grok-4-1-fast-reasoning

Grok Code Fast Models​

  • xai:grok-code-fast-1 - Speedy and economical reasoning model optimized for agentic coding (256K context)
  • xai:grok-code-fast - Alias for grok-code-fast-1
  • xai:grok-code-fast-1-0825 - Specific version of the code-fast model (256K context)

Grok-4 Fast Models​

  • xai:grok-4-fast-reasoning - Fast reasoning model with 2M context window
  • xai:grok-4-fast-non-reasoning - Fast non-reasoning model for instant responses (2M context)
  • xai:grok-4-fast - Alias for grok-4-fast-reasoning
  • xai:grok-4-fast-latest - Alias for grok-4-fast-reasoning

Grok-4 Models​

  • xai:grok-4-0709 - Flagship reasoning model (256K context)
  • xai:grok-4 - Alias for latest Grok-4 model
  • xai:grok-4-latest - Alias for latest Grok-4 model

Grok-3 Models​

  • xai:grok-3-beta - Latest flagship model for enterprise tasks (131K context)
  • xai:grok-3-fast-beta - Fastest flagship model (131K context)
  • xai:grok-3-mini-beta - Smaller model for basic tasks, supports reasoning effort (32K context)
  • xai:grok-3-mini-fast-beta - Faster mini model, supports reasoning effort (32K context)
  • xai:grok-3 - Alias for grok-3-beta
  • xai:grok-3-latest - Alias for grok-3-beta
  • xai:grok-3-fast - Alias for grok-3-fast-beta
  • xai:grok-3-fast-latest - Alias for grok-3-fast-beta
  • xai:grok-3-mini - Alias for grok-3-mini-beta
  • xai:grok-3-mini-latest - Alias for grok-3-mini-beta
  • xai:grok-3-mini-fast - Alias for grok-3-mini-fast-beta
  • xai:grok-3-mini-fast-latest - Alias for grok-3-mini-fast-beta

Grok-2 and previous Models​

  • xai:grok-2-latest - Latest Grok-2 model (131K context)
  • xai:grok-2-vision-latest - Latest Grok-2 vision model (32K context)
  • xai:grok-2-vision-1212
  • xai:grok-2-1212
  • xai:grok-beta - Beta version (131K context)
  • xai:grok-vision-beta - Vision beta version (8K context)

You can also use specific versioned models:

  • xai:grok-2-1212
  • xai:grok-2-vision-1212

Configuration​

The provider supports all OpenAI provider configuration options plus Grok-specific options. Example usage:

promptfooconfig.yaml
# yaml-language-server: $schema=https://promptfoo.dev/config-schema.json
providers:
  - id: xai:grok-3-mini-beta
    config:
      temperature: 0.7
      reasoning_effort: 'high' # Only for grok-3-mini models
      apiKey: your_api_key_here # Alternative to XAI_API_KEY

Reasoning Support​

Multiple Grok models support reasoning capabilities:

Grok Code Fast Models: The grok-code-fast-1 family are reasoning models optimized for agentic coding workflows. They support:

  • Function calling and tool usage
  • Web search via search_parameters
  • Fast inference with built-in reasoning

Grok-3 Models: The grok-3-mini-beta and grok-3-mini-fast-beta models support reasoning through the reasoning_effort parameter:

  • reasoning_effort: "low" - Minimal thinking time, using fewer tokens for quick responses
  • reasoning_effort: "high" - Maximum thinking time, leveraging more tokens for complex problems
info

For Grok-3, reasoning is only available for the mini variants. The standard grok-3-beta and grok-3-fast-beta models do not support reasoning.

Grok 4.1 Fast Specific Behavior​

Grok 4.1 Fast is xAI's frontier model specifically optimized for agentic tool calling:

  • Two variants: grok-4-1-fast-reasoning for maximum intelligence, grok-4-1-fast-non-reasoning for instant responses
  • Massive context window: 2,000,000 tokens for handling complex multi-turn agent interactions
  • Optimized for tool calling: Trained specifically for high-performance agentic tool calling via RL in simulated environments
  • Low latency and cost: $0.20/1M input tokens, $0.50/1M output tokens with fast inference
  • Unsupported parameters: Same restrictions as Grok-4 (no presence_penalty, frequency_penalty, stop, reasoning_effort)
promptfooconfig.yaml
# yaml-language-server: $schema=https://promptfoo.dev/config-schema.json
providers:
  - id: xai:grok-4-1-fast-reasoning
    config:
      temperature: 0.7
      max_completion_tokens: 4096

Grok-4 Fast Specific Behavior​

Grok-4 Fast models offer the same capabilities as Grok-4 but with faster inference and lower cost:

  • Two variants: grok-4-fast-reasoning for reasoning tasks, grok-4-fast-non-reasoning for instant responses
  • 2M context window: Same large context as Grok 4.1 Fast
  • Same parameter restrictions as Grok-4: No presence_penalty, frequency_penalty, stop, or reasoning_effort
promptfooconfig.yaml
# yaml-language-server: $schema=https://promptfoo.dev/config-schema.json
providers:
  - id: xai:grok-4-fast-reasoning
    config:
      temperature: 0.7
      max_completion_tokens: 4096

Grok-4 Specific Behavior​

Grok-4 introduces significant changes compared to previous Grok models:

  • Always uses reasoning: Grok-4 is a reasoning model that always operates at maximum reasoning capacity
  • No reasoning_effort parameter: Unlike Grok-3 mini models, Grok-4 does not support the reasoning_effort parameter
  • Unsupported parameters: The following parameters are not supported and will be automatically filtered out:
    • presencePenalty / presence_penalty
    • frequencyPenalty / frequency_penalty
    • stop
  • Larger context window: 256,000 tokens compared to 131,072 for Grok-3 models
  • Uses max_completion_tokens: As a reasoning model, Grok-4 uses max_completion_tokens instead of max_tokens
promptfooconfig.yaml
# yaml-language-server: $schema=https://promptfoo.dev/config-schema.json
providers:
  - id: xai:grok-4
    config:
      temperature: 0.7
      max_completion_tokens: 4096

Grok Code Fast Specific Behavior​

The Grok Code Fast models are optimized for agentic coding workflows and offer several key features:

  • Built for Speed: Designed to be highly responsive for agentic coding tools where multiple tool calls are common
  • Economical Pricing: At $0.20/1M input tokens and $1.50/1M output tokens, significantly more affordable than flagship models
  • Reasoning Capabilities: Built-in reasoning for code analysis, debugging, and problem-solving
  • Tool Integration: Excellent support for function calling, tool usage, and web search
  • Coding Expertise: Particularly adept at TypeScript, Python, Java, Rust, C++, and Go
promptfooconfig.yaml
# yaml-language-server: $schema=https://promptfoo.dev/config-schema.json
providers:
  - id: xai:grok-code-fast-1
    # or use the alias:
    # - id: xai:grok-code-fast
    config:
      temperature: 0.1 # Lower temperature often preferred for coding tasks
      max_completion_tokens: 4096
      search_parameters:
        mode: auto # Enable web search for coding assistance

Region Support​

You can specify a region to use a region-specific API endpoint:

providers:
  - id: xai:grok-2-latest
    config:
      region: us-west-1 # Will use https://us-west-1.api.x.ai/v1

This is equivalent to setting base_url="https://us-west-1.api.x.ai/v1" in the Python client.

Live Search (Beta)​

Deprecation Notice

xAI has announced that the Live Search API (via search_parameters) will be deprecated by December 15, 2025. The replacement is the Agent Tools API, which provides enhanced agentic search capabilities. Agent Tools require the Responses API endpoint - see the Agent Tools API section for more details.

You can optionally enable Grok's Live Search feature to let the model pull in real-time information from the web or X. Pass a search_parameters object in your provider config. The mode field controls how search is used:

  • off – Disable search
  • auto – Model decides when to search (default)
  • on – Always perform live search

Additional fields like sources, from_date, to_date, and return_citations may also be provided.

promptfooconfig.yaml
providers:
  - id: xai:grok-3-beta
    config:
      search_parameters:
        mode: auto
        return_citations: true
        sources:
          - type: web

For a full list of options see the xAI documentation.

Agent Tools API (Responses API)​

Use the xai:responses:<model> provider to access xAI's Agent Tools API, which enables autonomous server-side tool execution for web search, X search, and code interpretation.

promptfooconfig.yaml
providers:
  - id: xai:responses:grok-4-1-fast-reasoning
    config:
      temperature: 0.7
      max_output_tokens: 4096
      tools:
        - type: web_search
        - type: x_search

Available Agent Tools​

ToolDescription
web_searchSearch the web and browse pages
x_searchSearch X posts, users, and threads
code_interpreterExecute Python code in a sandbox
collections_searchSearch uploaded knowledge bases
mcpConnect to remote MCP servers

Web Search Tool​

tools:
  - type: web_search
    filters:
      allowed_domains:
        - example.com
        - news.com
      # OR excluded_domains (cannot use both)
    enable_image_understanding: true

X Search Tool​

tools:
  - type: x_search
    from_date: '2025-01-01' # ISO8601 format
    to_date: '2025-11-27'
    allowed_x_handles:
      - elonmusk
    enable_image_understanding: true
    enable_video_understanding: true

Code Interpreter Tool​

tools:
  - type: code_interpreter
    container:
      pip_packages:
        - numpy
        - pandas

Complete Example​

promptfooconfig.yaml
providers:
  - id: xai:responses:grok-4-fast
    config:
      temperature: 0.7
      tools:
        - type: web_search
          enable_image_understanding: true
        - type: x_search
          from_date: '2025-01-01'
        - type: code_interpreter
          container:
            pip_packages:
              - numpy
      tool_choice: auto # auto, required, or none
      parallel_tool_calls: true

tests:
  - vars:
      question: What's the latest AI news? Search the web and X.
    assert:
      - type: contains
        value: AI

Responses API Configuration​

ParameterTypeDescription
temperaturenumberSampling temperature (0-2)
max_output_tokensnumberMaximum tokens to generate
top_pnumberNucleus sampling parameter
toolsarrayAgent tools to enable
tool_choicestringTool selection mode: auto, required, none
parallel_tool_callsbooleanAllow parallel tool execution
instructionsstringSystem-level instructions
previous_response_idstringFor multi-turn conversations
storebooleanStore response for later retrieval
response_formatobjectJSON schema for structured output

Supported Models​

The Responses API works with Grok 4 models:

  • grok-4-1-fast-reasoning (recommended for agentic workflows)
  • grok-4-1-fast-non-reasoning
  • grok-4-fast-reasoning
  • grok-4-fast-non-reasoning
  • grok-4

If you're using Live Search via search_parameters, migrate to the Responses API before December 15, 2025:

Before (Live Search - deprecated):

providers:
  - id: xai:grok-4-1-fast-reasoning
    config:
      search_parameters:
        mode: auto
        sources:
          - type: web
          - type: x

After (Responses API):

providers:
  - id: xai:responses:grok-4-1-fast-reasoning
    config:
      tools:
        - type: web_search
        - type: x_search

Deferred Chat Completions​

Not Yet Supported

xAI offers Deferred Chat Completions for long-running requests that can be retrieved asynchronously via a request_id. This feature is not yet supported in promptfoo. For async workflows, use the xAI Python SDK directly.

Function Calling​

xAI supports standard OpenAI-compatible function calling for client-side tool execution:

promptfooconfig.yaml
providers:
  - id: xai:grok-4-1-fast-reasoning
    config:
      tools:
        - type: function
          function:
            name: get_weather
            description: Get the current weather for a location
            parameters:
              type: object
              properties:
                location:
                  type: string
                  description: City and state
              required:
                - location

Structured Outputs​

xAI supports structured outputs via JSON schema:

promptfooconfig.yaml
providers:
  - id: xai:grok-4
    config:
      response_format:
        type: json_schema
        json_schema:
          name: analysis_result
          strict: true
          schema:
            type: object
            properties:
              summary:
                type: string
              confidence:
                type: number
            required:
              - summary
              - confidence
            additionalProperties: false

You can also load schemas from external files:

config:
  response_format: file://./schemas/analysis-schema.json

Nested file references and variable rendering are supported (see OpenAI documentation for details).

Vision Support​

For models with vision capabilities, you can include images in your prompts using the same format as OpenAI. Create a prompt.yaml file:

prompt.yaml
- role: user
  content:
    - type: image_url
      image_url:
        url: '{{image_url}}'
        detail: 'high'
    - type: text
      text: '{{question}}'

Then reference it in your promptfoo config:

promptfooconfig.yaml
# yaml-language-server: $schema=https://promptfoo.dev/config-schema.json
prompts:
  - file://prompt.yaml

providers:
  - id: xai:grok-2-vision-latest

tests:
  - vars:
      image_url: 'https://example.com/image.jpg'
      question: "What's in this image?"

Image Generation​

xAI also supports image generation through the Grok image model:

providers:
  - xai:image:grok-2-image

Example configuration for image generation:

promptfooconfig.yaml
# yaml-language-server: $schema=https://promptfoo.dev/config-schema.json
prompts:
  - 'A {{style}} painting of {{subject}}'

providers:
  - id: xai:image:grok-2-image
    config:
      n: 1 # Number of images to generate (1-10)
      response_format: 'url' # 'url' or 'b64_json'

tests:
  - vars:
      style: 'impressionist'
      subject: 'sunset over mountains'

Video Generation​

xAI supports video generation through the Grok Imagine API using the xai:video:grok-imagine-video provider:

promptfooconfig.yaml
# yaml-language-server: $schema=https://promptfoo.dev/config-schema.json
prompts:
  - 'Generate a video of: {{scene}}'

providers:
  - id: xai:video:grok-imagine-video
    config:
      duration: 5 # 1-15 seconds
      aspect_ratio: '16:9'
      resolution: '720p'

tests:
  - vars:
      scene: a cat playing with yarn
    assert:
      - type: cost
        threshold: 1.0

Configuration Options​

OptionTypeDefaultDescription
durationnumber8Video length in seconds (1-15)
aspect_ratiostring16:9Aspect ratio: 16:9, 4:3, 1:1, 9:16, 3:4, 3:2, 2:3
resolutionstring720pOutput resolution: 720p, 480p
poll_interval_msnumber10000Polling interval in milliseconds
max_poll_time_msnumber600000Maximum wait time (10 minutes)

Image-to-Video​

Animate a static image by providing an image URL:

providers:
  - id: xai:video:grok-imagine-video
    config:
      image:
        url: 'https://example.com/image.jpg'
      duration: 5

Video Editing​

Edit an existing video with text instructions:

providers:
  - id: xai:video:grok-imagine-video
    config:
      video:
        url: 'https://example.com/source-video.mp4'

prompts:
  - 'Make the colors more vibrant and add slow motion'
note

Video editing skips duration, aspect ratio, and resolution validation since these are determined by the source video.

Pricing​

Video generation is billed at approximately $0.05 per second of generated video.

Voice Agent API​

The xAI Voice Agent API enables real-time voice conversations with Grok models via WebSocket. Use the xai:voice:<model> provider format.

providers:
  - xai:voice:grok-3

Configuration​

promptfooconfig.yaml
# yaml-language-server: $schema=https://promptfoo.dev/config-schema.json
providers:
  - id: xai:voice:grok-3
    config:
      voice: 'Ara' # Ara, Rex, Sal, Eve, or Leo
      instructions: 'You are a helpful voice assistant.'
      modalities: ['text', 'audio']
      websocketTimeout: 60000 # Connection timeout in ms
      tools:
        - type: web_search
        - type: x_search

Available Voices​

VoiceDescription
AraFemale voice
RexMale voice
SalMale voice
EveFemale voice
LeoMale voice

Built-in Tools​

The Voice API includes server-side tools that execute automatically:

ToolDescription
web_searchSearch the web for information
x_searchSearch posts on X (Twitter)
file_searchSearch uploaded files in vector stores
tools:
  - type: web_search
  - type: x_search
    allowed_x_handles:
      - elonmusk
      - xai
  - type: file_search
    vector_store_ids:
      - vs-123
    max_num_results: 10

Custom Function Tools and Assertions​

You can define custom function tools inline or load them from external files:

promptfooconfig.yaml
providers:
  - id: xai:voice:grok-3
    config:
      # Inline tool definition
      tools:
        - type: function
          name: set_volume
          description: Set the device volume level
          parameters:
            type: object
            properties:
              level:
                type: number
                description: Volume level from 0 to 100
            required:
              - level

      # Or load from external file (YAML or JSON)
      # tools: file://tools.yaml

tests:
  - vars:
      question: 'Set the volume to 50 percent'
    assert:
      # Check that the correct function was called with correct arguments
      - type: javascript
        value: |
          const calls = output.functionCalls || [];
          return calls.some(c => c.name === 'set_volume' && c.arguments?.level === 50);

      # Or use tool-call-f1 for function name matching
      - type: tool-call-f1
        value: ['set_volume']
        threshold: 1.0

External tools file example:

tools.yaml
- type: function
  name: get_weather
  description: Get the current weather for a location
  parameters:
    type: object
    properties:
      location:
        type: string
    required:
      - location

- type: function
  name: set_reminder
  description: Set a reminder for the user
  parameters:
    type: object
    properties:
      message:
        type: string
      time:
        type: string
    required:
      - message
      - time

When function tools are used, the provider output includes a functionCalls array with:

  • name: The function name that was called
  • arguments: The parsed arguments object
  • result: The result returned by your function handler (if provided)

Custom Endpoint Configuration​

You can configure a custom WebSocket endpoint for the Voice API, useful for proxies or regional endpoints:

providers:
  - id: xai:voice:grok-3
    config:
      # Option 1: Full base URL (transforms https:// to wss://)
      apiBaseUrl: 'https://my-proxy.example.com/v1'

      # Option 2: Host only (builds https://{host}/v1)
      # apiHost: 'my-proxy.example.com'

You can also use the XAI_API_BASE_URL environment variable:

export XAI_API_BASE_URL=https://my-proxy.example.com/v1

URL transformation: The provider automatically converts HTTP URLs to WebSocket URLs (https:// → wss://, http:// → ws://) and appends /realtime to reach the Voice API endpoint.

Complete WebSocket URL Override​

For advanced use cases like local testing, custom proxies, or endpoints requiring query parameters, you can provide a complete WebSocket URL that will be used exactly as specified without any transformation:

providers:
  - id: xai:voice:grok-3
    config:
      # Use this URL exactly as-is (no transformation applied)
      websocketUrl: 'wss://custom-endpoint.example.com/path?token=xyz&session=abc'

This is useful for:

  • Local development and testing with mock servers
  • Custom proxy configurations
  • Adding authentication tokens or session IDs as URL parameters
  • Using alternative WebSocket gateways or regional endpoints

Audio Configuration​

Configure input/output audio formats:

config:
  audio:
    input:
      format:
        type: audio/pcm
        rate: 24000
    output:
      format:
        type: audio/pcm
        rate: 24000

Supported formats: audio/pcm, audio/pcmu, audio/pcma Supported sample rates: 8000, 16000, 22050, 24000, 32000, 44100, 48000 Hz

Complete Example​

promptfooconfig.yaml
# yaml-language-server: $schema=https://promptfoo.dev/config-schema.json
prompts:
  - file://input.json

providers:
  - id: xai:voice:grok-3
    config:
      voice: 'Ara'
      instructions: 'You are a helpful voice assistant.'
      modalities: ['text', 'audio']
      tools:
        - type: web_search

tests:
  - vars:
      question: 'What are the latest AI developments?'
    assert:
      - type: llm-rubric
        value: Provides information about recent AI news

Pricing​

The Voice Agent API is billed at $0.05 per minute of connection time.

For more information on the available models and API usage, refer to the xAI documentation.

Examples​

For examples demonstrating text generation, image creation, and web search, see the xai example.

npx promptfoo@latest init --example xai

For real-time voice conversations with Grok, see the xai-voice example.

npx promptfoo@latest init --example xai-voice

See Also​

Troubleshooting​

502 Bad Gateway Errors​

If you encounter 502 Bad Gateway errors when using the xAI provider, this typically indicates:

  • An invalid or missing API key
  • Server issues on x.ai's side

The xAI provider will provide helpful error messages to guide you in resolving these issues.

Solution: Verify your XAI_API_KEY environment variable is set correctly. You can obtain an API key from https://x.ai/.

Controlling Retries​

If you're experiencing timeouts or want to control retry behavior:

  • To disable retries for 5XX errors: PROMPTFOO_RETRY_5XX=false
  • To reduce retry delays: PROMPTFOO_REQUEST_BACKOFF_MS=1000 (in milliseconds)

Reference​