Direct API callers must set the anthropic-version header to 2026-10-21; SDK users must upgrade to SDK releases that use the new version. The Python package named in the guide is anthropic 2.0.0.
The release contains breaking changes to the Messages API. Document blocks sent directly in assistant messages now return a 400 error, as do non-empty citations arrays on text blocks in user messages. The temperature, top_p, and top_k request parameters have been removed and return 400 errors if sent. Anthropic says no replacement setting is provided for non-default sampling values.
The migration also removes older field names from Admin API and Claude Enterprise Analytics API responses, including roles in favor of role_ids and name in favor of display_name. API-key workspace_id is replaced by scope. The source does not establish a mandatory retirement date for the older API version, migration uptake, or the operational effect on individual applications.