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Claude releases an API version and changes defaults in new SDK and CLI releases

On 21 October 2026, Claude released an API version affecting businesses using its SDKs or ant CLI. New tool releases default to that version and include breaking changes.

1 min read Source: platform.claude.com

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What changed: Claude released API version 2026-10-21. New client SDK and ant CLI releases send this API version by default. These tool releases also include breaking changes independent of the API version.

Who is affected

The source does not specify business types; the changes concern Claude API client SDKs and the ant CLI.

What it means for your business

For businesses using Claude API SDKs or the ant CLI, upgrading these tools changes the default API version and requires assessing compatibility changes independently of the selected API version.

What to do

Identify your SDK or ant CLI version; review the linked API migration guide and SDK/CLI changes before upgrading.

When it takes effect

The new API, SDK and CLI versions were released on 21 October 2026; the source specifies no migration deadline.

Source: https://platform.claude.com/docs/en/release-notes/overview#october-21-2026

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