xAI / Grok

Use the xai provider for xAI Grok models. xAI supports both web_search and x_search; fast-agent sends x_search as xAI's provider-managed X Search tool.

Sign in with a Grok/X subscription

fast-agent auth login xai

The device login opens an xAI verification URL and displays a code. Provider credentials use the OS keyring when it is writable and otherwise fall back to ~/.fast-agent/auth.json. Access tokens refresh automatically before expiry.

The model selector also offers this login when an xAI model is selected without a configured credential.

Useful credential commands:

fast-agent auth status xai
fast-agent auth token xai
fast-agent auth export xai ./xai.auth.json
fast-agent auth logout xai

An exported file contains only the selected provider and includes its refresh token. Set FAST_AGENT_AUTH_FILE to use that portable file. This is the recommended form for long-running Harbor jobs because refreshed credentials are written back to the staged file.

Configure

xai:
  api_key: "${XAI_API_KEY}"
  # base_url: "https://api.x.ai/v1" # default

Environment variables:

• XAI_API_KEY: Your xAI API key
• XAI_BASE_URL: Override the API endpoint
• FAST_AGENT_AUTH_FILE: Explicit portable provider credential file

An explicit xai.api_key or XAI_API_KEY takes precedence over stored OAuth.

Use a model

fast-agent --model "xai.grok-4.3?reasoning=high"
fast-agent --model "xai.grok-4.3?web_search=on"
fast-agent --model "xai.grok-4.3?x_search=on"
fast-agent --model "xai.grok-4.5"

Reasoning and search tools

Useful xAI query parameters:

• reasoning=none|low|medium|high on reasoning-capable Grok models
• web_search=on|off for xAI web search
• x_search=on|off for xAI's X Search remote tool

web_search and x_search are distinct provider-managed tools.

Capabilities

Capabilities are model-dependent. See Models Reference for fast-agent's known structured output, reasoning, modality, and tool metadata.

Model aliases