Claude API Version 2026-10-21

The first new official Claude API version since 2023, with a few breaking changes, for developers who call the Claude API directly or through Anthropic's SDKs.

Details

Opt in by setting the API version header to 2026-10-21, or by upgrading to the new major versions of the Anthropic SDKs and the ant command-line tool, which use it by default
Removes the temperature, top_p, and top_k settings from the Messages API
Sending documents in assistant turns or citations in user turns now returns an error, and a few deprecated Admin and Enterprise Analytics API fields are replaced
The previous version, 2023-06-01, is not deprecated, so existing integrations keep working
Anthropic plans to release versions more often so breaking changes can be handled before a new model requires them. The /claude-api skill in Claude Code can update existing code to the new version