// 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-fast"
}).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-fast"
}).then(response => {
document.body.innerHTML = response.message.content;
});
</script>
</body>
</html>
# pip install openai
from openai import OpenAI
client = OpenAI(
base_url="https://api.puter.com/puterai/openai/v1/",
api_key="YOUR_PUTER_AUTH_TOKEN",
)
response = client.chat.completions.create(
model="x-ai/grok-4-fast",
messages=[
{"role": "user", "content": "Explain quantum computing in simple terms"}
],
)
print(response.choices[0].message.content)
curl https://api.puter.com/puterai/openai/v1/chat/completions \
-H "Content-Type: application/json" \
-H "Authorization: Bearer YOUR_PUTER_AUTH_TOKEN" \
-d '{
"model": "x-ai/grok-4-fast",
"messages": [
{"role": "user", "content": "Explain quantum computing in simple terms"}
]
}'
Model Card
Grok 4 Fast is an optimized variant delivering performance similar to Grok 4 but using 40% fewer thinking tokens with a massive 2 million token context window. It offers up to 64x cost reduction versus early frontier models like OpenAI's o3.
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 Sep 19, 2025
Model Playground
Try Grok 4 Fast instantly in your browser.
This playground uses the Puter.js AI API — no API keys or setup required.
Benchmarks
How Grok 4 Fast performs on standard evaluations.
| Benchmark | Score |
|---|---|
| GPQA Diamond Graduate-level science Q&A | 60.6% |
| Humanity's Last Exam Cross-domain reasoning | 5.0% |
| LiveCodeBench Recent coding problems | 40.1% |
| SciCode Scientific programming | 32.9% |
| AIME 2025 Advanced math exam | 41.3% |
| IFBench Instruction following | 37.7% |
| LCR Long-context reasoning | 20.0% |
| Terminal-Bench Hard Agentic terminal tasks | 12.1% |
| τ²-Bench Tool use / agents | 63.7% |
Scores sourced from Artificial Analysis.
Find other xAI models →
Grok Build 0.1
Grok Build 0.1 is xAI's fast coding model trained specifically for agentic software engineering workflows. Released in May 2026 and currently in early access, it is purpose-built for interactive coding agents, tool use, and multi-step development tasks rather than general-purpose conversation. The model accepts text and image inputs and produces text output, with a 256,000-token context window. It supports function calling, structured outputs, and built-in reasoning that is always active, enabling it to think through problems before responding. Developers building AI coding agents, automated code review pipelines, or multi-step development tools will find it a strong fit. At $1/M input and $2/M output tokens, it offers an accessible price point for agentic, high-throughput use cases.
ChatGrok 4.3
Grok 4.3 is xAI's latest flagship reasoning model, designed for agentic workflows, instruction following, and tasks demanding high factual accuracy. It accepts text and image inputs with always-on reasoning that cannot be disabled. The model supports a 1 million token context window with no output token limit, making it well suited for long-document analysis and multi-step agent tasks. Priced at $1.25 per million input tokens and $2.50 per million output tokens, it delivers improved cost-efficiency over its predecessor Grok 4.20 — scoring higher on the Artificial Analysis Intelligence Index while costing roughly 20% less to run. Grok 4.3 showed a major jump in real-world agentic task performance, gaining over 300 Elo points on GDPval-AA versus Grok 4.20. It also scores 98% on τ²-Bench Telecom and 81% on IFBench. A strong pick for developers building cost-sensitive agent systems that need reliable tool use and instruction adherence.
ChatGrok 4.20
Grok 4.20 is xAI's flagship large language model, offering a rare combination of low hallucination rates and high throughput at competitive pricing. It achieved a record 78% non-hallucination rate on the Artificial Analysis Omniscience benchmark — the highest of any model tested — making it a strong choice for applications where factual reliability matters more than peak reasoning scores. It scored 78.5% on GPQA Diamond and 87.3% on MATH-500. The model supports a 2M-token context window, text and image inputs, parallel function calling, structured outputs, and built-in web search. Reasoning can be toggled on or off per request via API parameter. At $2 per million input tokens and $6 per million output tokens, it's one of the most affordable frontier models available, with output speeds exceeding 230 tokens per second.
Frequently Asked Questions
You can access Grok 4 Fast 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.
Yes, it is free if you're using it through Puter.js. With the User-Pays Model, you can add Grok 4 Fast to your app at no cost — your users pay for their own AI usage directly, making it completely free for you as a developer.
| Price per 1M tokens | |
|---|---|
| Input | $0.2 |
| Output | $0.5 |
Grok 4 Fast was created by xAI and released on Sep 19, 2025.
Grok 4 Fast supports a context window of 2M tokens. For reference, that is roughly equivalent to 4,000 pages of text.
Grok 4 Fast can generate up to 2M tokens in a single response.
Grok 4 Fast has a knowledge cutoff date of Jul 2025. This means the model was trained on data available up to that date.
Grok 4 Fast accepts the following input types: text, image. It produces: text.
Yes, Grok 4 Fast supports tool use (function calling), allowing it to interact with external tools, APIs, and data sources as part of its response flow.
Grok 4 Fast scores 23.1 on the Artificial Analysis Intelligence Index, outperforming 55% of tracked models. On coding, it scores 19.0 (outperforms 49% of models). On math, it scores 41.3 (outperforms 42% of models).
Yes — the Grok 4 Fast 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.
Get started with Puter.js
Add Grok 4 Fast to your app without worrying about API keys or setup.
Read the Docs View Tutorials