Claude Sonnet 5 launched with 1M token context and adaptive thinking

We've launched Claude Sonnet 5 (claude-sonnet-5), the next generation of our Sonnet model family, at introductory pricing of $2 / $10 per MTok through August 31, 2026 (standard $3 / $15 thereafter). Claude Sonnet 5 supports a 1M token context window, 128k max output tokens, and the same set of tools and platform features as Claude Sonnet 4.6, except Priority Tier, which is not available. Key behavior changes: adaptive thinking is now on by default; manual extended thinking is removed and returns a 400 error; setting sampling parameters (temperature, top_p, top_k) to non-default values returns a 400 error. Claude Sonnet 5 uses a new tokenizer that produces approximately 30% more tokens for the same text.