Do I have to upgrade to Claude API version 2026-10-21 right away?

Anthropic's migration guide tells developers who rely on a non-default temperature, top_p or top_k to either stop sending the parameter or keep that request on 2023-06-01, so the older Claude API version still answers requests. Older SDK major versions keep sending 2023-06-01, which means nothing changes until a team installs the new SDK major or changes the anthropic-version header itself.

What happens to temperature on Claude API version 2026-10-21?

On Claude API version 2026-10-21, any request that sends temperature, top_p or top_k gets a 400 error, even at the default value. Requests then sample with the defaults, including a temperature of 1.0. Claude 4.7 and later models already accept only the defaults, so they behave as before, but on a model such as Claude Sonnet 4.6 a lowered temperature loses its effect.

Does Claude API version 2026-10-21 work on Amazon Bedrock?

Anthropic's migration guide says Claude API version 2026-10-21 is available on Amazon Bedrock only for Claude 4.7 and later models. Developers who call Opus 4.6 or an earlier model on Bedrock should stay on their current SDK version or keep sending their current API version, and move those calls to a Claude 4.7 or later model before upgrading.

Why did the Anthropic SDK license change?

The new Anthropic SDK and ant CLI major versions released with API version 2026-10-21 are licensed under the Apache License 2.0, while earlier versions remain under the MIT License. Anthropic's migration guide says no code changes are needed for the license switch, but teams that track the licenses of their dependencies should update their records.

Anthropic · 2026-10-21 · major

Claude API version 2026-10-21 — first new version since 2023, with breaking changes

Anthropic released Claude API version 2026-10-21, the first since 2023-06-01. It removes temperature, top_p and top_k, renames Admin API fields, and ships new major SDKs that default to it and move from MIT to Apache 2.0.

Claude Platform docs card for the guide to migrating to API version 2026-10-21

Anthropic's first new API version in three years drops the sampling knobs and comes with a new major SDK in every language.

Quick facts

Maker	Anthropic
New version	anthropic-version: 2026-10-21
Replaces	2023-06-01
Python / TypeScript SDK	anthropic 2.0.0 / @anthropic-ai/sdk 1.0.0
Other SDKs	C# 13.0.0, Go 2.0.0, Java 3.0.0, PHP 1.0.0, Ruby 2.0.0, ant CLI 2.0.0
SDK license	Apache 2.0 (was MIT)

What is it?

Claude API version 2026-10-21 is the first new value for the anthropic-version header since 2023-06-01. A request on the new version returns a 400 error if it sends temperature, top_p or top_k, puts a document block directly in an assistant message, or sends citations on text blocks in a user message. Admin API and Claude Enterprise Analytics API responses also drop the old names of renamed fields, such as workspace_id on API keys, which becomes scope.

How does it work?

Each SDK sends the API version that was current when its major version shipped, so moving to 2026-10-21 means installing the new major release listed in the facts table, or setting the header by hand for raw HTTP calls. The new SDKs also change their own interfaces: MessageParam becomes one type per role, the legacy Text Completions API is gone from the TypeScript, Go, Java and Ruby SDKs and the CLI, and the ant CLI no longer accepts --api-key or --auth-token flags.

Why does it matter?

Code that pins a lower temperature for consistent output will break on the new version, and Anthropic says no other setting replaces it. Teams that need those values can keep the affected requests on 2023-06-01. The Go SDK and CLI move to new /v2 module paths, and the license switch to Apache 2.0 matters to anyone who tracks the licenses of their dependencies.

Who is it for?

developers and platform teams calling the Claude API directly or through an SDK

Frequently asked questions

Do I have to upgrade to Claude API version 2026-10-21 right away?: Anthropic's migration guide tells developers who rely on a non-default temperature, top_p or top_k to either stop sending the parameter or keep that request on 2023-06-01, so the older Claude API version still answers requests. Older SDK major versions keep sending 2023-06-01, which means nothing changes until a team installs the new SDK major or changes the anthropic-version header itself.
What happens to temperature on Claude API version 2026-10-21?: On Claude API version 2026-10-21, any request that sends temperature, top_p or top_k gets a 400 error, even at the default value. Requests then sample with the defaults, including a temperature of 1.0. Claude 4.7 and later models already accept only the defaults, so they behave as before, but on a model such as Claude Sonnet 4.6 a lowered temperature loses its effect.
Does Claude API version 2026-10-21 work on Amazon Bedrock?: Anthropic's migration guide says Claude API version 2026-10-21 is available on Amazon Bedrock only for Claude 4.7 and later models. Developers who call Opus 4.6 or an earlier model on Bedrock should stay on their current SDK version or keep sending their current API version, and move those calls to a Claude 4.7 or later model before upgrading.
Why did the Anthropic SDK license change?: The new Anthropic SDK and ant CLI major versions released with API version 2026-10-21 are licensed under the Apache License 2.0, while earlier versions remain under the MIT License. Anthropic's migration guide says no code changes are needed for the license switch, but teams that track the licenses of their dependencies should update their records.

Try it

pip install --upgrade 'anthropic>=2.0.0'