Anthropic API Version 2026-10-21: Every Breaking Change and How to Upgrade the SDKs
Anthropic's first new API version since 2023-06-01 shipped Oct 21, 2026 with Python SDK 2.0.0, TypeScript 1.0.0 and other majors. temperature/top_p/top_k now return 400, keys go out as Authorization: Bearer, and MessageParam is a union. Here is how to fix each error.