Claude API update brings breaking SDK migration changes
Anthropic released API version 2026-10-21 in its October 21 release notes, alongside major client updates. Python SDK 2.0.0, TypeScript SDK 1.0.0 and the ant CLI 2.0.0 request that version by default. The announcement also lists new C#, Go, Java, PHP and Ruby SDK versions.
Those new SDK and CLI releases use Apache 2.0 and include breaking changes independent of the API version.
What changes in API requests
The version reference lists availability on the Claude API, Claude Platform on AWS, Microsoft Foundry and Google Cloud. Amazon Bedrock support is limited to Claude 4.7 and later models.
Under the new API version, sending temperature, top_p or top_k returns HTTP 400 on every model. Document blocks directly inside assistant messages are also rejected. User text blocks with populated citation arrays are rejected, including those nested in search results.
Admin and Enterprise Analytics responses also remove older field names. For example, API key responses replace workspace_id with a scope object. Workspace keys expose their real workspace identifier there, including the Default Workspace. Organization wide keys have no workspace identifier in that object.
An SDK upgrade needs separate checks
The migration guide explains the client changes. The new SDKs and CLI generally move API keys from X-Api-Key to the Authorization header using the Bearer scheme. Gateways inspecting the older header need review. The API accepts either header. Foundry retains its existing key header.
The ant CLI also removes flags that accept a key or auth token directly as an argument. Documented alternatives include environment variables and standard input. Earlier releases retain MIT licensing.
Check behavior before switching
Removing sampling settings leaves their defaults. On older models that supported other values, an application loses that customization. The guide allows those requests to remain on 2023-06-01. Older Bedrock models must retain their existing SDK or API version until the model changes.
Anthropic recommends testing and shipping code fixes with the upgrade. ByteForward reviewed documentation without installing releases or running migration tests.
Related coverage explains Claude customer profiles and beta enforcement webhooks.
Illustrative archival photo. Spring 2012 Student Hackathon Coding by @matylda for hackNY.org, via Wikimedia Commons, licensed under Creative Commons Attribution ShareAlike 2.0.
