Grok 4.1 Fast

Claims and evidence

• Released 19 November 2025 ● Primary source[1]header [2]November 2025, Nov 19
• Retired 15 May 2026Effective 12:00 PM PT on the xAI API. ● Primary source[3]first paragraph

• Status Retiredgrok-4-1-fast-reasoning and grok-4-1-fast-non-reasoning retired from the xAI API; requests are served by grok-4.3. ● Primary source[3]list of retired models
• Replaced by Grok 4.3The reasoning slug redirects to grok-4.3 with low reasoning effort, the non-reasoning slug with reasoning effort none. ● Primary source[3]Recommended Replacements

• Successor of Grok 4 Fast EditorialEditorial link along the Fast tier: the announcement compares Grok 4.1 Fast with Grok 4 Fast but does not call it a successor. ● Primary source[1]

• Change · Tool use Trained with reinforcement learning in simulated environments with tools from dozens of domains, and launched with the server-side Agent Tools API.Compared with Grok 4 Fast ● Primary source[1]Trained for the real world; Agent Tools API
• Change · Context length Long-horizon multi-turn reinforcement learning aimed at steady performance across the full 2-million-token window; the window size is unchanged.Compared with Grok 4 Fast ● Primary source[1]
• Change · Other xAI reports a lower hallucination rate than Grok 4 Fast.Compared with Grok 4 Fast ● Primary source[1]

• Feature Reasoning modeReleased as grok-4-1-fast-reasoning and grok-4-1-fast-non-reasoning. ● Primary source[1]Start Building
• Feature Tool usePositioned for tool calling; launched with the server-side Agent Tools API. ● Primary source[1]Trained for the real world; Agent Tools API
• Context window 2M tokens ● Primary source[1]introduction
• Parameters Not disclosedNot disclosed by xAI. No claim madeNo source
• Access API ● Primary source[1]introduction; Start Building [2]November 2025, Nov 19

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