Claude API version 2026-10-21 ships with new SDK major versions

what changed

On 21 October 2026, Anthropic released API version 2026-10-21. A migration guide on the Claude docs site explains how to upgrade.

New client SDKs and the ant CLI send that version by default. The versions are:

• Python SDK 2.0.0
• TypeScript SDK 1.0.0
• C# SDK 13.0.0
• Go SDK 2.0.0
• Java SDK 3.0.0
• PHP SDK 1.0.0
• Ruby SDK 2.0.0
• ant CLI 2.0.0

The notes also say the new SDK and CLI versions carry breaking changes that do not depend on the API version. They are now licensed under Apache 2.0 instead of the MIT License.

why it matters

A normal dependency bump can now change two things at once: the API version your code sends, and the SDK surface your code calls. Teams that let a tool such as a dependency bot merge major versions may find out in CI, or in production.

The licence change also matters to anyone who tracks licences in their dependency review. Apache 2.0 and MIT are both permissive, but a review process may still want to record the change.

what we would do

• Pin SDK versions today, so no automated update moves you to a major version unreviewed.
• Read the migration guide and list every breaking change that touches your code, in both the API version section and the SDK section.
• Upgrade one service first, behind your normal tests and evals, and compare behaviour before moving the rest.
• Tell your licence review owner about the Apache 2.0 change.

If you want help planning a migration across several services, see our build service.