[Late catch] Claude API 2026-10-21: the first new API version in three years, new major SDKs, and no more sampling parameters
What is it?
Anthropic released Claude API version 2026-10-21, the first new version since 2023-06-01. Under it, sending temperature, top_p, or top_k returns a 400 error even at default values, and so do document blocks in assistant messages and citations in user messages. New major SDK versions that send this version by default (Python 2.0.0, TypeScript 1.0.0, Go 2.0.0, Java 3.0.0, and others) shipped alongside it, as did ant CLI 2.0.0.
pip install -U "anthropic>=2.0.0"Why does it matter?
Upgrading the SDK alone changes your API version, so teams with automatic dependency updates are affected immediately. Code that pins output with sampling parameters, proxies that read the X-Api-Key header, and scripts that use old Admin API field names all need changes. The SDK license also moved from MIT to Apache 2.0. On Amazon Bedrock, the new version works only with Claude 4.7 and later models.
Maturity
GAThe API version and SDKs are generally available. The old 2023-06-01 version still works, so there's no rush to migrate.
How to track it
- SDK follow-ups: watch GitHub releases of the Python 2.x and TypeScript 1.x SDKs for further compatibility fixes.
- Coverage: check the migration guide for wider support on the Amazon Bedrock and Google Cloud clients.
- Old version: watch the release notes for any end-of-support date for 2023-06-01.