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Grok 4 Fast Reasoning

xaixai/grok-4-fast-reasoning

xAI's fast reasoning model with 2M token context window. Combines speed with strong reasoning capabilities, supporting text and image inputs with function calling and structured outputs.

Context Length
2M
Max Output
128K
Input Price
$0.360/ 1M tokens
Output Price
$0.900/ 1M tokens

Modalities

textimage→text

Pricing Breakdown

TypeRate
Input$0.360 / 1M tokens
Output$0.900 / 1M tokens

Supported Parameters

temperaturemax_tokenstop_ptoolstool_choiceresponse_formatreasoningstop

API Usage Examples

China users: replace api.therouter.ai with api.therouter.com.cn in the examples below for lower latency.

cURL
curl https://api.therouter.ai/v1/chat/completions   -H "Content-Type: application/json"   -H "Authorization: Bearer $THE_ROUTER_API_KEY"   -d '{
    "model": "xai/grok-4-fast-reasoning",
    "messages": [
      {"role": "user", "content": "Summarize the key points from this input."}
    ]
  }'