Deyron Labs graphic: Claude API version 2026-10-21 removes temperature, top_p and top_k, new SDK major versions under Apache 2.0

What happened

On 21 October 2026 Anthropic’s release notes recorded: “We’ve released API version 2026-10-21.” Developers select an API version with the anthropic-version request header, and the versioning page now lists 2026-10-21 with a migration guide. Anthropic makes Claude, the AI tool that helped draft this article, so please read this as a company describing its own changes.

Key details

Everything below comes from Anthropic’s versioning page and release notes, checked on 22 October 2026. We did not read the full migration guide or run any API calls.

  • Messages API changes listed: a document block inside an assistant message returns a 400 error; citations in a user message returns a 400 error; and the temperature, top_p and top_k parameters are removed and “return 400 on every model”.
  • Other changes listed: renamed fields in the Admin API and Enterprise Analytics, and new enforcement_status and enforcement_actions fields on user profiles.
  • New SDK versions: Python 2.0.0, TypeScript 1.0.0, C# 13.0.0, Go 2.0.0, Java 3.0.0, PHP 1.0.0, Ruby 2.0.0 and the ant CLI 2.0.0.
  • Licence: the release notes say the SDKs are licensed under Apache 2.0 instead of the MIT License.
  • Older version: the pages we read list the previous version header (2023-06-10) without a deprecation date. A developer newsletter summary says Anthropic plans more frequent versions so teams can handle breaking changes before a new model requires them; we did not find that statement on the pages we read.

Why it matters

Code that sets temperature, top_p or top_k will fail with errors if it is moved to the new version header, so those calls need removing as part of the upgrade. Nothing in the pages we read says existing integrations on the older header stop working, so the change is something teams can schedule rather than an emergency.

The SDK licence change from MIT to Apache 2.0 matters mostly to companies with open-source compliance rules, because the two licences differ on patent terms and notices. Check the migration guide before upgrading production services.

Disclosure: Claude, made by Anthropic, was one of the AI tools used to research and draft this article, and this article is about Anthropic. Details are Anthropic’s own documentation and have not been independently verified.

Sources

  1. Claude API release notes, 21 October 2026 Primary source , Anthropic
  2. API versioning Primary source , Anthropic
  3. Migrating to API version 2026-10-21 Primary source , Anthropic