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Claude Sonnet 5.5 now available

Model launch · 2026-09-29

Claude Sonnet 5.5 is available on OneFast as claude-sonnet-5-5.

Sonnet 5.5 is Anthropic's balanced Claude model for coding, agents and long-document work. Use it through:

  • the Anthropic Messages API (/v1/messages) — including Claude Code;
  • the OpenAI-compatible endpoint (/v1/chat/completions).

Prompt caching and extended thinking are supported. See the model catalog for the live price.