Grok 4 Fast Reasoning API

Grok 4 Fast with always-on reasoning for complex problem-solving tasks.
Context
2M tokens
Input
$0.26 / 1M
Output
$0.65 / 1M

How to use Grok 4 Fast Reasoning API

Install any OpenAI-compatible SDK, point it at api.aimlapi.com/v1, and set the model to x-ai/grok-4-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-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-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-fast-reasoning","messages":[{"role":"user","content":"Hello!"}]}'

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

Grok 4 Fast Reasoning API Pricing

TypePrice
Input
$0.26 / 1M tokens
Output
$0.65 / 1M tokens

Grok 4 Fast Reasoning Benchmarks

BenchmarkScoreWhat it measures
AIME 2025
92%
Competition mathematics (AIME), 2025
GPQA Diamond
85.7%
Google-proof graduate science questions (hardest subset)

Grok 4 Fast Reasoning vs other models

ModelInputOutputContextBest for
$0.26 / 1M
$0.65 / 1M
2M tokens
Coding + agents
$6.5 / 1M
$39 / 1M
1.05M tokens
Reasoning + agents
$2.6 / 1M
$13 / 1M
1M tokens
Balanced coding + agents
$3.9 / 1M
$19.5 / 1M
1M tokens
Long-context, multimodal & agentic workflows
$0.65 / 1M
$3.9 / 1M
1.05M tokens
Reasoning + agents

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