Grok 4.1 Fast Reasoning API

x-ai/grok-4-1-fast-reasoning
Grok 4.
Context
2M tokens
Input
$1.625 / 1M tokens
Output
$3.25 / 1M tokens
Released
Nov 20, 2025

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.

Grok 4.1 Fast Reasoning API Pricing

TypePrice
Input
$1.625 / 1M tokens
Output
$3.25 / 1M tokens
Cached input
$0.26 / 1M tokens

Grok 4.1 Fast Reasoning Benchmarks

BenchmarkScoreWhat it measuresSourceRetrieved
Intelligence
20.4
Composite score across standardised reasoning, knowledge and problem-solving evaluations, measured independently by Artificial AnalysisSourceSeptember 12, 2026
Math
89.3
Composite score across standardised mathematics evaluations, measured independently by Artificial AnalysisSourceSeptember 12, 2026

Frequently asked questions

Grok 4.1 Fast Reasoning has a 2,000,000 tokens context window and can return up to 1,999,000 tokens.

Grok 4.1 Fast Reasoning takes image, text as input and returns text.

Use x-ai/grok-4-1-fast-reasoning as the model id. Requests go to https://api.aimlapi.com/v1/chat/completions.

Grok 4.1 Fast Reasoning is priced at input $1.625 / 1M tokens, output $3.25 / 1M tokens, cached input $0.26 / 1M tokens.

Yes, Grok 4.1 Fast Reasoning can stream responses as they are generated.

Yes, Grok 4.1 Fast Reasoning accepts image input alongside text.

Grok 4.1 Fast Reasoning was built by xAI .

Yes, it supports function calling as one of its core capabilities.

Start building with Grok 4.1 Fast Reasoning

Get API Key
1000+ models, one API.