Claude API version 2026-10-21 removes temperature, top_p and top_k, Anthropic's first new API version since 2023

Anthropic has released version 2026-10-21 of the Claude API, the first new entry in its API version history since 2023-06-01. Developers opt in by sending the header anthropic-version: 2026-10-21, and SDK users move to it by upgrading to the SDK major versions that first use it. The 2023-06-01 version is not deprecated.

WHAT BREAKS

Per Anthropic's version history and migration guide, read directly: on the new version the temperature, top_p and top_k request parameters are removed, and a request that sends any of them returns a 400 error on every model. Placing a document block directly in an assistant message also returns a 400, as does a text block with a non-empty citations array in a user message. Several Admin API fields are renamed; API keys, for example, now return scope.workspace_id instead of workspace_id. The Claude Enterprise Analytics API renames actor.email to actor.email_address.

WHERE IT WORKS

The Claude API, Claude Platform on AWS, Microsoft Foundry and Google Cloud. On Amazon Bedrock it is available for Claude 4.7 and later models; calls to older Bedrock models should stay on the version they send today.

WHAT WE DO NOT KNOW

How long 2023-06-01 will stay supported, since Anthropic gives no end date, and whether an upcoming model will require the new version.