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Documentation Index

Fetch the complete documentation index at: https://docs.anyfast.ai/llms.txt

Use this file to discover all available pages before exploring further.

Claude Sonnet 4.5 Thinking is the extended thinking variant of Claude Sonnet 4.5, available through Anyfast via an OpenAI-compatible interface. It combines Sonnet 4.5’s excellent balance of speed and capability with step-by-step internal reasoning enabled by default, delivering improved accuracy on complex tasks while maintaining fast response times.

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Key capabilities

  • OpenAI-compatible — Works as a drop-in replacement with the OpenAI SDK
  • Extended thinking — Step-by-step internal reasoning enabled by default
  • Best coding model — Top performance on code generation, refactoring, and debugging
  • Enhanced reasoning — Improved accuracy on complex, multi-step tasks
  • Long context — Handles large documents and multi-turn conversations
  • Streaming — Supports real-time token streaming via SSE

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Quick example

curl https://www.anyfast.ai/v1/messages \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-sonnet-4-5-20250929-thinking",
    "messages": [
      { "role": "user", "content": "Solve step by step: If a train travels 120 km in 2 hours, then slows down and travels 80 km in 3 hours, what is the average speed for the entire trip?" }
    ]
  }'

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Parameters

ParameterTypeRequiredDescription
modelstringYesMust be claude-sonnet-4-5-20250929-thinking
messagesarrayYesList of { role, content } objects
max_tokensintegerNoMaximum tokens to generate
temperaturefloatNo0–2. Controls randomness. Default: 1
streambooleanNoEnable SSE streaming. Default: false
top_pfloatNoNucleus sampling threshold. Default: 1
stopstring / arrayNoSequences that stop generation

API Reference

View the interactive API playground for Claude Sonnet 4.5 Thinking.