Anthropic put out a new Claude API version on 21 October, labeled 2026-10-21, according to a thread from its Claude developer account on X. It is the company’s first official version since 2023, even though the API has changed a great deal in that time. Anthropic says versions will now arrive more often, so developers can handle breaking changes ahead of the next model launch.
The thread’s second post lists three changes. The Messages API no longer takes top_p, top_k or temperature, the dials that control how random a model’s answers are. Requests that put documents in assistant turns, or citations in user turns, now get a 400 error back. A few deprecated fields in the Admin and Enterprise Analytics APIs are replaced.
Nobody has to move yet, because the older 2023-06-01 version is not deprecated. But the new major releases of Anthropic’s SDKs and its ant command-line tool default to the new version, so a routine upgrade can switch it on. Any team that sets those randomness dials should pin its API version in code before bumping an SDK.
Reported by Anthropic’s Claude developer account on X, 21 October 2026.
