Grok 4 Fast Reasoning
Grok 4 Fast Reasoning is a text generation model from X.ai designed for rapid reasoning tasks with a 2,000,000 token context window.
X.aiFast reasoning with a 2M token context
Grok 4 Fast Reasoning is a large language model developed by X.ai, the AI division associated with xAI. It is part of the Grok 4 model family and is specifically configured for fast reasoning, meaning it is optimized to produce reasoned responses with lower latency compared to standard reasoning variants. The model supports a context window of up to 2,000,000 tokens, which allows it to process and reference very long documents or extended conversation histories within a single session.
The model is suited for tasks that benefit from structured reasoning at speed, such as multi-step problem solving, code analysis, and working through lengthy documents or datasets. Its 2,000,000 token maximum response size matches its context window, meaning it can in principle generate very long outputs in a single call. Grok 4 Fast Reasoning is available through MindStudio without requiring separate API key management, making it accessible for developers building AI-powered applications.
What Grok 4 Fast Reasoning supports
Fast Reasoning
Produces reasoned, multi-step responses with reduced latency compared to standard reasoning modes. Suited for logic, analysis, and structured problem solving.
Long Context Window
Supports up to 2,000,000 tokens of context, enabling processing of very long documents, codebases, or extended conversation histories in a single session.
Extended Output Length
Can generate responses up to 2,000,000 tokens in a single call, accommodating tasks that require lengthy or detailed outputs.
Code Analysis
Applies reasoning capabilities to code review, debugging, and multi-file analysis, leveraging the large context window to handle full codebases.
Text Generation
Generates natural language text for a wide range of tasks including summarization, drafting, and question answering over long-form content.
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Get Started FreeBenchmark scores
Scores represent accuracy — the percentage of questions answered correctly on each test.
| Benchmark | What it tests | Score |
|---|---|---|
| MMLU-Pro | Expert knowledge across 14 academic disciplines | 85.0% |
| GPQA Diamond | PhD-level science questions (biology, physics, chemistry) | 84.7% |
| LiveCodeBench | Real-world coding tasks from recent competitions | 83.2% |
| HLE | Questions that challenge frontier models across many domains | 17.0% |
| SciCode | Scientific research coding and numerical methods | 44.2% |
Common questions about Grok 4 Fast Reasoning
What is the context window size for Grok 4 Fast Reasoning?
Grok 4 Fast Reasoning supports a context window of 2,000,000 tokens, allowing very long documents or conversations to be processed in a single session.
How does Grok 4 Fast Reasoning differ from standard Grok 4?
Grok 4 Fast Reasoning is specifically configured for faster reasoning responses. It is designed to reduce latency on reasoning tasks compared to non-fast variants, while retaining the same large context window.
What is the pricing for Grok 4 Fast Reasoning on MindStudio?
Published pricing for Grok 4 Fast Reasoning is not listed in the available metadata. You can check MindStudio's pricing page or your account dashboard for current usage costs.
What is the knowledge cutoff for Grok 4 Fast Reasoning?
A specific knowledge cutoff date is not included in the available metadata for this model. X.ai has not publicly confirmed a cutoff date in the information provided here.
Does Grok 4 Fast Reasoning support image or video inputs?
Based on the available metadata, image and video analysis support is not confirmed for Grok 4 Fast Reasoning. The model is listed as a text generation model with no confirmed multimodal input types.
When was Grok 4 Fast Reasoning released?
Grok 4 Fast Reasoning has a listed release date of September 2025 and was added to MindStudio on March 11, 2026.
What people think about Grok 4 Fast Reasoning
Community discussion around Grok 4 Fast is generally positive, with users highlighting its cost efficiency relative to comparable models. One widely shared thread noted that Grok 4 Fast matches high-level performance benchmarks at a fraction of the cost of models like Claude Opus 4.1.
Discussions also touch on its competitive benchmark scores and real-world arena rankings, though some threads veer into broader AI capability debates rather than focusing specifically on Grok 4 Fast. Use cases mentioned include research, reasoning tasks, and cost-sensitive production deployments.
Poetiq Achieves SOTA on ARC-AGI 2 Public Eval
Grok 4 Fast matches same high-level performance as Claude Opus 4.1, at less than 1% of the cost
Documentation & links
Parameters & options
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