Tools #Anthropic Oct 22, 2026 · Originally published Oct 21

Claude API ships 2026-10-21, its first new version since 2023-06-01: temperature, top_p and top_k now return errors, and new major SDKs move to Apache 2.0

A genuinely breaking upgrade. Which requests now fail with a 400, what changed in the SDKs' defaults, and which requests should stay on the old version for now.

Primary source Claude Platform Docs · platform.claude.com Read the original ↗

// Key points

On 2026-10-21, a request that sends temperature, top_p or top_k returns a 400, even at the default value. Claude 4.7 and later models already accept only the defaults and sample as before, but on models such as Claude Sonnet 4.6 a lowered temperature loses its effect, and nothing replaces it.
Document blocks placed directly in assistant messages, and text blocks with non-empty citations in user messages, also return a 400.
Python SDK 2.0.0, TypeScript SDK 1.0.0, Go SDK 2.0.0, Java SDK 3.0.0, ant CLI 2.0.0 and the other new versions send 2026-10-21 by default and are licensed under Apache 2.0 instead of MIT.
The new SDKs send the API key as Authorization: Bearer instead of X-Api-Key, so proxies and gateways that read or set X-Api-Key need to change. Requests that rely on non-default sampling can stay on 2023-06-01.

Builder's takeI'd pin the SDK major version first so an automatic dependency bump can't take production down, then grep every repo for temperature and X-Api-Key. AI Interview's scoring calls lowered temperature for consistency; those either stay on 2023-06-01 for now or move to a JSON Schema plus a scoring rubric, with a fixed question set to check the score distribution before switching.

// Background · from #Anthropic

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