Claude API returns 400 after upgrading the Anthropic SDK (Python 2.0 / TypeScript 1.0): temperature, top_p, top_k or citations no longer accepted

Anthropic released API version 2026-10-21 on 2026-10-21 with new major SDKs that send it automatically: Python anthropic 2.0.0, TypeScript @anthropic-ai/sdk 1.0.0, C# 13.0.0, Go v2.0.0, Java 3.0.0, PHP 1.0.0, Ruby 2.0.0, ant CLI 2.0.0. Under 2026-10-21 these requests return 400: - temperature, top_p or top_k in Messages or Batch requests, even at default values. Remove them (the new SDKs no longer have them). Claude 4.7 and later already only used the defaults, so output doesn't change; on older models that accepted other values, a lowered temperature has no replacement. - a document block placed directly in an assistant message: send documents in user messages. - a text block with a non-empty citations array in a user message: remove citations from those blocks (citations on assistant text blocks are still fine). Also changed: the new SDKs and CLI send the API key as Authorization: Bearer <key> instead of X-Api-Key, so update proxies, gateways, log filters or test stubs that read X-Api-Key. The API accepts either header. If you need a non-default temperature, keep that request on anthropic-version: 2023-06-01 (stay on the previous SDK major, or set the header yourself) while you migrate. Sources: https://platform.claude.com/docs/en/api/migration-2026-10-21 ; https://platform.claude.com/docs/en/release-notes/api