Anthropic releases a new Claude API version dated October 21, 2026, its first official version since 2023, with breaking changes and new major SDKs
API version 2026-10-21 is now available. The Claude API has evolved a lot, but this is our first official version release since 2023. We plan to release versions more often so you can handle breaking changes before a new model requires them. 2023-06-01 is not deprecated.
Context
Developers get a clear upgrade path and warning before breaking changes, which matters as more products depend on the Claude API.
The Claude API uses a version header so that existing code keeps working while the API changes. The previous official version dated June 1, 2023 is not deprecated, according to Anthropic.
Deep dive
On October 21, ClaudeDevs posted that a new API version is available. It said the Claude API has evolved a lot, but this is the first official version release since 2023, and that Anthropic plans to release versions more often so developers can handle breaking changes before a new model requires them. It added that the 2023 version is not deprecated.
Anthropic's migration guide lists the breaking changes. In the Messages API, the temperature, top_p and top_k parameters are removed and return an error on every model, document blocks placed directly in assistant messages return an error, and text blocks with citations in user messages return an error. Several Admin API and Enterprise Analytics API fields were renamed.
The release notes say new SDK and CLI versions send the new version by default, including Python SDK 2.0.0, TypeScript SDK 1.0.0, Go SDK 2.0.0 and the ant CLI 2.0.0, and that they now use the Apache 2.0 license instead of MIT. The docs say the version is available on the Claude API and major cloud platforms, and on Amazon Bedrock only for Claude 4.7 and later models.
What to expect next
Watch how quickly developers move to the new SDK major versions, and whether removing sampling parameters such as temperature causes friction for apps that relied on them. Anthropic says it will release versions more often, so watch for the next one and whether it arrives ahead of a new model. Also watch whether the older 2023 version gets a deprecation date.