Name: Grok 4.1 Fast Reasoning API
Brand: xAI

Overview

What is Grok 4.1 Fast Reasoning API?

Grok 4.1 Fast is a frontier multimodal model optimized for high-performance agentic tool calling with advanced reasoning capabilities.

Technical Specifications
- Supported inputs: Image, Text
- Output: Text
- Context window: 2,000,000 tokens / Max output: 1,999,000 tokens
- Endpoint: /chat/completions

Performance Benchmarks
[embed]

Grok 4.1 Fast Reasoning API Pricing
- Input: $0.26 / 1M tokens
- Output: $0.65 / 1M tokens

Where to Use Grok 4.1 Fast Reasoning

Coding and code review
Generate, debug, and review code across languages, reading whole files or repos in a single prompt.

Agentic and multi-step workflows
Reliable tool-calling and instruction-following suit agent loops that plan, call tools, and iterate.

Long-document analysis
Summarize and extract from contracts, papers, and reports without aggressive chunking.

Code Sample
[embed]

Uptime and performance

Uptime (24h): 100%
Uptime (7d): 98.0%
Availability (24h): 100%
Error rate (24h): 0%
End-to-end latency (24h median): 10.0s
Time to first token (24h median): 2.1s
Throughput (24h median): 93.0 tok/s

Measured on the AI/ML API gateway across live traffic. Figures are medians unless stated. Last updated 2026-10-12.

Use cases

Grok 4.1 Fast Reasoning is documented as suited to customer support, where it is described as handling complex real-world support tasks with fast, accurate agentic reasoning. It is also suited to finance, where the same source says it excels in complex real-world finance use cases.

It is suited to deep research and agentic search workflows, with documentation describing it as a production-grade agent model for tool calling and agentic search. It is also suited to rapid multi-step reasoning and structured decision-making, especially in analysis pipelines and other applications that need fast responses without losing reasoning depth.

How to use Grok 4.1 Fast Reasoning API

Install any OpenAI-compatible SDK, point it at api.aimlapi.com/v1, and set the model to x-ai/grok-4-1-fast-reasoning.

import requests

r = requests.post(
    "https://api.aimlapi.com/v1/chat/completions",
    headers={"Authorization": "Bearer " + AIMLAPI_KEY},
    json={
      "model": "x-ai/grok-4-1-fast-reasoning",
      "messages": [
        {
          "role": "user",
          "content": "Hello!"
        }
      ]
    },
)
print(r.json())

const r = await fetch("https://api.aimlapi.com/v1/chat/completions", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${process.env.AIMLAPI_KEY}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "model": "x-ai/grok-4-1-fast-reasoning",
    "messages": [
      {
        "role": "user",
        "content": "Hello!"
      }
    ]
  }),
});
console.log(await r.json());

curl -X POST https://api.aimlapi.com/v1/chat/completions \
  -H "Authorization: Bearer $AIMLAPI_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"x-ai/grok-4-1-fast-reasoning","messages":[{"role":"user","content":"Hello!"}]}'

OpenAI-compatible — swap the base URL and it works with your existing SDK.