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Claude Opus 4.1 Thinking is the extended thinking variant of Claude Opus 4.1, available through AnyFast via an OpenAI-compatible interface. It combines Opus’s unmatched intelligence with step-by-step internal reasoning enabled by default, delivering the highest accuracy available on the most demanding tasks including advanced mathematics, scientific research, and complex architectural decisions.

Key capabilities

  • OpenAI-compatible — Works as a drop-in replacement with the OpenAI SDK
  • Extended thinking — Step-by-step internal reasoning enabled by default
  • Maximum intelligence — The most capable reasoning model available
  • Deep analysis — Excels at advanced math, science, and complex problem solving
  • Long context — Handles large documents and multi-turn conversations
  • Streaming — Supports real-time token streaming via SSE

Quick example

Thinking sampling compatibility: For reliable requests, omit temperature and top_k. Anthropic accepts the unchanged default temperature: 1 and top_p values from 0.95 to 1. A non-default temperature, any top_k, or a top_p below 0.95 returns a 400 error while Thinking is enabled. See Anthropic’s Thinking limits and API usage primer.

Parameters

API Reference

View the interactive API playground for Claude Opus 4.1 Thinking.