Anthropic's new Claude API version rejects sampling controls that older integrations could send, even at their default values. Major software development kit upgrades select the new version automatically. Document placement, message citations and authentication headers also change, making the application code and its client library part of the same migration. Older Bedrock models can remain on their existing version.
Anthropic has changed the application programming interface, or API, used to call Claude models. The new version removes the temperature, top_p and top_k sampling controls. Requests containing them receive a 400 error even when the values match former defaults. With the fields omitted, temperature stays at 1. Anthropic’s new major software development kits select the changed API version automatically.[1], [2]
Documents placed directly inside assistant messages must move to user messages. Documents nested in tool results remain accepted. Nonempty citations arrays on user text blocks are rejected, while assistant citations and enabled citations on documents or search results remain supported. The Admin API also renames role, group and scope fields, distinguishing organization-wide keys from keys tied to a workspace.[1]
The new client libraries send keys through Authorization: Bearer. Although the API still accepts X-Api-Key, proxies checking only that older header require adjustment. Message types split by role, and legacy Completions interfaces disappear from several kits. On Amazon Bedrock, the new version supports Claude 4.7 and later; older models can retain their previous SDK and API version. Anthropic recommends testing the application changes together with the library upgrade before deployment.[1]
