The default behavior of extended thinking in Claude 4 models returns a summary of Claude's full thinking process, with the full thinking encrypted and returned in the signature field of thinking block output.
We've launched interleaved thinking in public beta, a feature that enables Claude to think in between tool calls. To enable interleaved thinking, use the beta headerinterleaved-thinking-2025-05-14.
We've launched the Files API in public beta, enabling you to upload files and reference them in the Messages API and code execution tool.
We've launched the Code execution tool in public beta, a tool that enables Claude to execute Python code in a secure, sandboxed environment.
We've launched the MCP connector in public beta, a feature that allows you to connect to remote MCP servers directly from the Messages API.
To increase answer quality and decrease tool errors, we've changed the default value for the top_pnucleus sampling parameter in the Messages API from 0.999 to 0.99 for all models. To revert this change, set top_p to 0.999.
Additionally, when extended thinking is enabled, you can now set top_p to values between 0.95 and 1.