whats-new-sonnet-5 changedmodels/sonnet-5/whats-new-sonnet-5
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44description: Overview of new features and behavior changes in Claude Sonnet 5.
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7<Note>
8 Claude Sonnet 5.5 is the current Sonnet model. See [What's new in Claude Sonnet 5.5](https://platform.claude.com/docs/en/models/sonnet-5-5/whats-new-sonnet-5-5).
9</Note>
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711Claude Sonnet 5 is the next generation of Anthropic's Sonnet model family. It is a drop-in upgrade for Claude Sonnet 4.6 with three behavior changes: [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking) is on by default, manual extended thinking now returns a 400 error (it was deprecated on Claude Sonnet 4.6), and setting sampling parameters (`temperature`, `top_p`, `top_k`) to non-default values returns a 400 error. This page summarizes everything new at launch, including a new tokenizer.
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913## New model
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