Anthropic releases Claude API version 2026-10-21, with breaking changes

Anthropic's ClaudeDevs account announced API version 2026-10-21, which it calls the first official Claude API version release since 2023. Anthropic says it plans to release versions more often, so developers can handle breaking changes before a new model requires them. The older version, 2023-06-01, is not deprecated.

Changes Anthropic lists for the new version:

• temperature, top_p and top_k are removed from the Messages API.
• Documents in assistant turns, and citations in user turns, return a 400 error.
• A few deprecated Admin and Enterprise Analytics API fields are replaced.

New major versions of the Anthropic SDKs and the ant CLI were released the same day and default to 2026-10-21. Anthropic points to a migration guide and says the /claude-api skill in Claude Code can help update code.