Claude API 2026-10-21: temperature and top_p removed, SDK migration guide

On October 21, 2026, Anthropic released the 2026-10-21 version of the Claude API and new major versions of the SDKs and CLI ant. The source does not provide the release time.

What it is and what it is not: an API update with breaking changes for some integrations, not the launch of a new model.

In this article you will see:

• which parameters are no longer accepted
• which SDKs send the new version by default
• how to check compatibility before the upgrade

Claude API 2026-10-21 requires reviewing requests

The new version removes temperature, top_p and top_k from Messages and Message Batches requests. Sending any of them returns a 400 error, even when the value was the default.

document blocks directly in assistant messages and citations in texts sent by the user also return a 400 error. Anthropic recommends checking the affected cases and testing the integration before publishing. (official migration guide)

Credit: Anthropic.

Seven SDKs and the ant CLI start using the new version

The first batch includes 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 ant CLI 2.0.0. They send version 2026-10-21 by default. (Anthropic release notes)

Anthropic also changed the license of these SDK and CLI versions from MIT to Apache 2.0. It is a license change, with no additional code required, but teams that track dependency licenses should update their inventories.

Migration depends on the runtime environment

On Amazon Bedrock, version 2026-10-21 is only available for Claude 4.7 and later models. Integrations with older models should keep the current SDK version or the API header they already use.

For another recent platform control change, read about Anthropic's inference hooks for Claude Enterprise. For context on models used by code agents, see Reflection's open model Beam.