Anthropic has launched Claude API version 2026-10-21, the first formal API version since 2023-06-01, according to its ClaudeDevs account. The headline change for developers: the Messages API no longer accepts the temperature, top_p and top_k sampling parameters.

The new version also returns a 400 error for documents passed in an assistant turn or citations in a user turn, and replaces some deprecated Admin and Enterprise Analytics API fields. New major versions of the Anthropic SDK and the ant CLI default to 2026-10-21 and ship with migration guides.

The old 2023-06-01 version is not deprecated, so existing integrations keep working. Anthropic says it will release API versions more frequently from here, so developers can absorb incompatible changes before new models require them.