Grok 4.1 Fast

Grok 4.1 Fast is positioned by xAI as its leading agentic tool-calling model, engineered for real-world agent workflows such as customer support automation and deep research assistance. Released on November 19, 2025, shortly after the consumer-facing Grok 4.1, the Fast variant was specifically designed for API-driven integrations rather than conversational consumer use. Its standout feature is an exceptionally long two-million-token context window, which allows the model to maintain awareness across very large documents, extended multi-turn dialogues, or lengthy chains of tool interactions without losing earlier context.

In practical terms, Grok 4.1 Fast is built around multi-turn tool orchestration, exposing reasoning and non-reasoning modes that developers can toggle via API parameters. The model integrates with xAI-hosted web search, X search, file retrieval, code execution, and MCP-compatible tools, making it well suited for building autonomous research agents and support assistants that need to pull from multiple external sources. Developers can pair the model's agent capabilities with structured output and temperature control for deterministic workflows. Note that the Grok 4.1 Fast API variants were retired on May 15, 2026, with their model slugs redirected to Grok 4.3, so this endpoint reflects historical rather than current xAI offerings.