Anthropic released API version 2026-10-21, its first since June 2023, and removed the temperature, top_p and top_k parameters
Under the new version a Messages or Batch request that sends any of the three sampling parameters returns a 400 error, as do document blocks placed in assistant messages and citations on text blocks in user messages; the Admin and Enterprise Analytics APIs rename several fields. The version ships with new SDK majors (Python 2.0.0, TypeScript 1.0.0, Go v2, C# 13.0.0, the ant CLI 2.0.0) that send it by default and drop the legacy Text Completions API, it is available on the Claude API, AWS, Microsoft Foundry and Google Cloud, and on Amazon Bedrock only for Claude 4.7 and later; requests pinned to 2023-06-01 keep working.
why it mattersBefore your next dependency bump, grep your codebase for temperature, top_p and top_k on Claude calls, since the new SDK majors will turn every one of them into a 400, and keep any call that relies on a lowered temperature on an older model pinned to the 2023-06-01 version.