X-Ai/Grok-4-Fast-Reasoning

xAIMCP Tool CallReasoning

xai/grok-4-fast-reasoningClosed API

Fast Grok model for responsive chat, reasoning, and tool-assisted work

Benchmark Pricing$0.20 / 1M in$0.50 / 1M out

Context: 2,000,000 tokens•Max Output: 2,000,000 tokens•Released: 2025-12-18

TECHNICAL SPECIFICATIONS

Context Window2,000,0002M tokens

Max Output2,000,0002M tokens

LicenseProprietaryCloud API only

Input Modalities

TextVisionAudioVideo

Function / Tool CallingSupported (MCP Ready)

Structured OutputsGuaranteed Schema

MODEL CONTEXT PROTOCOL (MCP) READINESS

✓ X-Ai/Grok-4-Fast-Reasoning natively supports OpenAI / Anthropic format tool calling and is fully compatible with MCP servers and agent loops.

MCP Context Window Recommendations

With a context capacity of 2,000,000 tokens, this model can handle extremely large MCP resource manifests, complete database schemas, and multiple active server tool definitions simultaneously without degradation.

API CALL INVOCATION EXAMPLE

// Example: Calling X-Ai/Grok-4-Fast-Reasoning via OpenAI SDK
import OpenAI from "openai";

const client = new OpenAI({
  apiKey: process.env.XAI_API_KEY,
});

const response = await client.chat.completions.create({
  model: "xai/grok-4-fast-reasoning",
  messages: [{ role: "user", content: "Hello! Can you inspect MCP tools?" }],
});

console.log(response.choices[0].message.content);