Anthropic removes temperature controls in new Claude API version

Anthropic’s new Claude API version does more than require code changes: it removes a way developers made some models’ answers more consistent. Version 2026-10-21 rejects temperature and two related settings, even at their default values. Teams that depend on custom values must drop them or keep those requests on the older version.

Anthropic’s migration guide sets out the switch from API version 2023-06-01. Direct callers select the new version through the anthropic-version request header. Updated major releases of its software development kits, or SDKs, and command-line interface select it automatically. For Python, the guide specifies upgrading the anthropic package to version 2.0.0.

One sampling default, no replacement knob

The removed settings are temperature, top_p and top_k. Sending any of them in Messages API or Message Batch requests produces a 400 error—a rejected request—even if the value matches the default. The updated SDKs and command-line interface also remove these settings from their supported inputs.

Without those parameters, requests use the defaults, including a temperature of 1.0. Anthropic says models that already accept only those defaults, such as Claude 4.7 and later, sample as before. But on models such as Claude Sonnet 4.6, lowering temperature previously offered more consistent output. That effect disappears under the new version, and no other setting replaces it.

Authentication shifts in the clients, not the API

The updated SDKs and command-line interface send API keys through Authorization: Bearer rather than X-Api-Key. The Claude API still accepts either header, so programs calling it directly need no authentication change. Proxies and gateways that read or set X-Api-Key must handle Authorization instead, or developers can explicitly restore the previous header behavior.

Message history and response readers need changes

The new version also rejects two message arrangements. These rules apply to Messages API calls, token counting and individual requests within batches created with the new version:

• Documents placed directly in assistant messages return a 400 error. Put them in user messages instead. Documents nested inside another block, such as a returned web-fetch tool result, remain accepted.
• User text blocks with non-empty citation arrays also return a 400 error, including inside search results. Citations in assistant replies remain accepted, as does enabling citations on documents and search results.

The Admin and Enterprise Analytics APIs stop returning old names for renamed fields, including roles becoming role_ids and actor.email becoming actor.email_address. API-key responses replace workspace_id with scope. Workspace-bound keys expose their actual workspace ID, including for the Default Workspace; keys covering all workspaces carry organization scope without a workspace_id.

On Amazon Bedrock, the new version is available only for Claude 4.7 and later models. Calls to older models must retain their existing SDK or API-version selection, or switch models first. Anthropic’s upgrade instructions call for releasing code fixes alongside the version change and testing the integration before release.