xAI: Grok 4.1 Fast (Reasoning)
x-ai/grok-4-1-fast-reasoning
Try Grok 4.1 Fast (Reasoning) for free in your browser, and add it to your app for free with Puter.js AI API.
Try it free Add to your app// npm install @heyputer/puter.js
import { puter } from '@heyputer/puter.js';
puter.ai.chat("Explain quantum computing in simple terms", {
model: "x-ai/grok-4-1-fast-reasoning"
}).then(response => {
document.body.innerHTML = response.message.content;
});
<html>
<body>
<script src="https://js.puter.com/v2/"></script>
<script>
puter.ai.chat("Explain quantum computing in simple terms", {
model: "x-ai/grok-4-1-fast-reasoning"
}).then(response => {
document.body.innerHTML = response.message.content;
});
</script>
</body>
</html>
Model Card
Grok 4.1 Fast (Reasoning) is xAI's reasoning-enabled variant of Grok 4.1 Fast, designed for tasks that benefit from extended chain-of-thought deliberation within a fast, agentic framework.
It shares the same model weights and 2M token context window as Grok 4.1 Fast but activates multi-step reasoning, making it well suited for complex problem solving, multi-hop analysis, and tasks where accuracy matters more than raw throughput. Reasoning effort is configurable via the API (low, medium, or high) to balance cost and quality.
The model supports text and image inputs, native tool use including web search and code execution, and parallel function calling. It cuts hallucination rates in half compared to Grok 4 Fast and is optimized for agentic workflows in enterprise domains such as customer support, finance, and research.
Context Window 2M
tokens
Max Output 2M
tokens
Input Cost $0.2
per million tokens
Output Cost $0.5
per million tokens
Input text, image
modalities
Tool Use Yes
Knowledge Cutoff Jul 2025
Release Date Nov 19, 2025
Try Grok 4.1 Fast (Reasoning) for free
Try Grok 4.1 Fast (Reasoning) instantly in your browser.
This playground uses the Puter.js AI API — no API keys or setup required.
Benchmarks
How Grok 4.1 Fast (Reasoning) performs on standard evaluations.
| Benchmark | Score |
|---|---|
| GPQA Diamond Graduate-level science Q&A | 85.3% |
| Humanity's Last Exam Cross-domain reasoning | 19.3% |
| LiveCodeBench Recent coding problems | 82.2% |
| AIME 2025 Advanced math exam | 89.3% |
| IFBench Instruction following | 52.7% |
| LCR Long-context reasoning | 74.0% |
| Terminal-Bench Hard Agentic terminal tasks | 24.2% |
| τ²-Bench Tool use / agents | 93.3% |
Scores sourced from Artificial Analysis.
Find other xAI models →
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ChatGrok 4.6
Grok 4.6 is xAI's frontier model for long-running agents and interactive, visual development work, built on the same 1.5-trillion-parameter V9 foundation as Grok 4.5 with additional supervised fine-tuning and reinforcement learning. It matches GPT-5.6 Sol on the Artificial Analysis Intelligence Index (both score 61) and leads on CursorBench v3.2 at 69.9%, with gains over Grok 4.5 across coding, research, and agentic benchmarks. xAI highlights it for vulnerability patching, engineering design work, and turning a rough product idea into a working first version, with improved self-testing on longer tasks. The model accepts text and image input with text-only output, a 500,000 token context window, and no output token limit. Reasoning effort is configurable across four levels (low, medium, high, xhigh), and it supports function calling, web search, X search, and code execution. At $2 per million input tokens and $6 per million output tokens, it costs the same as Grok 4.5.
ImageGrok Imagine Image 2.0
Grok Imagine Image 2.0 is xAI's second-generation text-to-image and image-editing model, released August 7, 2026 as the Quality Mode successor to Grok Imagine Image and Grok Imagine Image (Quality). It is built to produce images usable in real work rather than drafts: it follows instructions closely, plans typography and layout, and preserves elements across generations and edits. New editing tools include a magic wand for targeted region edits, segmentation for selecting precise areas, background removal with transparency, and multi-reference editing that accepts up to five input images in one generation. Smart resize recomposes an image across nine aspect ratios automatically. xAI reports it ranks second in the world on both the Arena text-to-image and image-edit leaderboards, behind OpenAI's gpt-image-2. It ships with ready-made templates for recurring workflows such as product shots, headshots, icons, and game assets, making it suited to product photography, e-commerce content, and character or marketing design work.
Frequently Asked Questions
You can access Grok 4.1 Fast (Reasoning) by xAI through Puter.js AI API. Include the library in your web app or Node.js project and start making calls with just a few lines of JavaScript — no backend and no configuration required. You can also use it with Python or cURL via Puter's OpenAI-compatible API.
Grok 4.1 Fast (Reasoning) is free to try with a Puter account. Every account includes a free AI allowance, and you can chat with it in the playground on this page. You can upgrade your account anytime for a larger allowance.
Grok 4.1 Fast (Reasoning) is free to integrate using the Puter.js AI API. With the User-Pays Model, you can add AI to your app for $0, since users cover their own AI usage through their Puter account.
| Price per 1M tokens | |
|---|---|
| Input | $0.2 |
| Output | $0.5 |
Grok 4.1 Fast (Reasoning) was created by xAI and released on Nov 19, 2025.
Grok 4.1 Fast (Reasoning) supports a context window of 2M tokens. For reference, that is roughly equivalent to 4,000 pages of text.
Grok 4.1 Fast (Reasoning) can generate up to 2M tokens in a single response.
Grok 4.1 Fast (Reasoning) has a knowledge cutoff date of Jul 2025. This means the model was trained on data available up to that date.
Grok 4.1 Fast (Reasoning) accepts the following input types: text, image. It produces: text.
Yes, Grok 4.1 Fast (Reasoning) supports tool use (function calling), allowing it to interact with external tools, APIs, and data sources as part of its response flow.
Grok 4.1 Fast (Reasoning) scores 20.4 on the Artificial Analysis Intelligence Index, outperforming 65% of tracked models. On math, it scores 89.3 (outperforms 88% of models).
Yes — the Grok 4.1 Fast (Reasoning) API works with any JavaScript framework, Node.js, or plain HTML through Puter.js. Just include the library and start building. See the documentation for more details.
Add Grok 4.1 Fast (Reasoning) to your app for free
Developers can integrate Grok 4.1 Fast (Reasoning) for free using the Puter.js AI API.
With the User-Pays Model, each user covers their own AI usage instead of the developer.