Chain-of-Thought Reasoning
Generates step-by-step reasoning traces for complex, multi-step problems. Reasoning mode is enabled by default in this variant of the model.
X.ai
Grok 4.1 Fast Reasoning
Grok 4.1 Fast Reasoning is a text generation model developed by xAI, the AI division of X. It is designed specifically for agentic and tool-calling workflows, trained through reinforcement learning in simulated environments across dozens of tool-use domains. The model supports a 2-million-token context window, accepts both text and image inputs, and produces text outputs with chain-of-thought reasoning enabled. The model is best suited for developers building autonomous agents, enterprise automation pipelines, and multi-step research or customer support applications. It supports structured outputs, function calling, and a range of tool integrations including web search, X search, code execution, file retrieval, and MCP tool integrations via the Agent Tools API. Its training cutoff is November 2025, and it is available through the xAI API as well as third-party cloud providers such as Oracle Cloud.
November 2025
N/A context
2,000,000 tokens output
Chain-of-Thought Reasoning
2M Token Context
Agentic Tool Calling
Structured Outputs
Multimodal Input
Fast Inference
Model Overview
High-signal model metadata in a structured two-column overview table.
Provider
The entity that provides this model.
X.ai
Input Context Window
The number of tokens supported by the input context window.
N/A
tokens
Maximum Output Tokens
The number of tokens that can be generated by the model in a single request.
2,000,000 tokens
tokens
Open Source
Whether the model's code is available for public use.
No
Release Date
When the model was first released.
November 2025
Knowledge Cut-off Date
When the model's knowledge was last updated.
November 2025
API Providers
The providers that offer this model. This is not an exhaustive list.
xAI API, OpenAI API
Modalities
Types of data this model can process.
Text
Image
Code
What is Grok 4.1 Fast Reasoning
A fuller summary of positioning, capabilities, and source-specific details for Grok 4.1 Fast Reasoning.
Grok 4.1 Fast Reasoning is a text generation model developed by xAI, the AI division of X. It is designed specifically for agentic and tool-calling workflows, trained through reinforcement learning in simulated environments across dozens of tool-use domains. The model supports a 2-million-token context window, accepts both text and image inputs, and produces text outputs with chain-of-thought reasoning enabled.
The model is best suited for developers building autonomous agents, enterprise automation pipelines, and multi-step research or customer support applications. It supports structured outputs, function calling, and a range of tool integrations including web search, X search, code execution, file retrieval, and MCP tool integrations via the Agent Tools API. Its training cutoff is November 2025, and it is available through the xAI API as well as third-party cloud providers such as Oracle Cloud.
Capabilities
What Grok 4.1 Fast Reasoning supports
2M Token Context
Supports a context window of up to 2 million tokens, enabling processing of very long documents or extended multi-turn agent sessions.
Agentic Tool Calling
Supports web search, X search, code execution, file retrieval, and MCP tool integrations through the Agent Tools API for autonomous task completion.
Structured Outputs
Returns structured JSON outputs and supports function calling via API, making it suitable for integration into typed application workflows.
Multimodal Input
Accepts both text and image inputs, producing text outputs, which allows it to handle tasks that involve visual content alongside written instructions.
Fast Inference
Optimized for low-latency responses relative to full reasoning models, making it practical for real-time or high-throughput agentic applications.
Pricing for Grok 4.1 Fast Reasoning
Primary API pricing shown in the same “quick compare” spirit as the reference page.
Input tokens
$0.20
Per million tokens
Output tokens
$2.50
Per million tokens
Price Comparison
Additional usage-cost dimensions synced into the project for this model.
maxTemperature
1
maxResponseSize
2,000,000 tokens
API Access & Providers
Places where this model is available, based on the synced detail-page metadata.
xAI API
OpenAI API
Model Performance
Benchmark scores synced from the current model source and normalized into the local catalog.
| Benchmark | Score |
|---|---|
|
GPQA Diamond
PhD-level science questions (biology, physics, chemistry)
|
|
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HLE
Questions that challenge frontier models across many domains
|
|
|
LiveCodeBench
Real-world coding tasks from recent competitions
|
|
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MMLU-Pro
Expert knowledge across 14 academic disciplines
|
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SciCode
Scientific research coding and numerical methods
|
Resources & Documentation
Official model cards, release notes, docs, and other references synced from the source page.
FAQ
Common questions about Grok 4.1 Fast Reasoning
What is the context window for Grok 4.1 Fast Reasoning?
Grok 4.1 Fast Reasoning supports a context window of up to 2 million tokens, which allows it to process very long documents or maintain extended multi-turn conversations within a single request.
What is the training data cutoff for this model?
The model's training data cutoff is November 2025, meaning it does not have knowledge of events or information published after that date unless provided via tool use or in-context retrieval.
How does the reasoning mode work in this model?
Grok 4.1 Fast Reasoning generates chain-of-thought reasoning traces as part of its response process, working through complex or multi-step problems before producing a final answer. This is the defining difference between this variant and the non-reasoning version of Grok 4.1 Fast.
What tools and integrations does this model support?
The model supports web search, X (Twitter) search, code execution, file retrieval, and MCP tool integrations through xAI's Agent Tools API. It also supports structured outputs and function calling via the standard API.
Where can I access Grok 4.1 Fast Reasoning?
The model is available through the xAI API and is also accessible via third-party cloud providers, including Oracle Cloud Infrastructure's Generative AI service.
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