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Claude Haiku 4.5 Thinking is the extended thinking variant of Claude Haiku 4.5, available through AnyFast via an OpenAI-compatible interface. It combines Haiku’s speed and cost-efficiency with step-by-step internal reasoning, delivering improved accuracy on complex tasks while remaining significantly faster and cheaper than larger thinking models.

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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
  • Fast + affordable — Thinking capability at Haiku-level speed and cost
  • Streaming — Supports real-time token streaming via SSE
  • Strong reasoning — Improved accuracy on math, logic, and multi-step problems

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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-haiku-4-5-20251001-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-haiku-4-5-20251001-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 Haiku 4.5 Thinking.