Anthropic released API version 2026-10-21 and new major SDK versions; applications need to review request parameters and authentication handling before upgrading.
The October 21 release and migration guide say that the new API version rejects temperature, top_p and top_k, returning a 400 error even when default values are supplied. The new SDKs and CLI use this API version by default and send API keys in Authorization: Bearer; the API still accepts the older X-Api-Key header. Teams should test gateways, request builders and response parsing before deployment. The official announcement supplies a date but no exact time.
