Anthropic ships Claude API version 2026-10-21, its first since 2023: temperature, top_p and top_k now return errors, new major SDKs switch to Bearer auth and Apache 2.0

Why it matters

【Key points】

Anthropic released Claude API version 2026-10-21 on Oct 21, the first new anthropic-version since 2023-06-01, with new major SDKs that send it by default.

1. SDKs: Python 2.0.0, TypeScript 1.0.0, C# 13.0.0, Go 2.0.0, Java 3.0.0, PHP 1.0.0, Ruby 2.0.0, ant CLI 2.0.0 (Python v2.0.0 tagged 15:51 UTC).

2. temperature, top_p and top_k now return a 400 error, even at defaults. Claude 4.7+ already only accepted defaults; older models such as Sonnet 4.6 lose low-temperature behavior with no replacement.

3. document blocks in assistant turns and citations in user turns now error; Admin and Enterprise Analytics API fields renamed; API-key workspace_id replaced by scope.

4. SDKs send keys as Authorization: Bearer, allow one credential per client, drop Text Completions, and move from MIT to Apache 2.0.

5. On Bedrock it covers only Claude 4.7+.

【Verifiable】

https://docs.anthropic.com/en/release-notes/api

https://docs.anthropic.com/en/api/migration-2026-10-21

https://github.com/anthropics/anthropic-sdk-python/releases/tag/v2.0.0

https://github.com/anthropics/anthropic-sdk-typescript/releases/tag/sdk-v1.0.0

【Our read】

1. Background: after three years on one version plus beta headers, this is Anthropic's first real cleanup, alongside this week's user profiles and org webhooks — the API is becoming an enterprise platform.

2. Comparison: OpenAI's reasoning models already reject temperature; Gemini keeps full sampling controls. Anthropic goes further by removing the parameters at the protocol level. Teams that relied on low temperature for extraction or reproducible evals need structured outputs, voting or another model.

3. Impact: default SDK users see little change, but gateways reading X-Api-Key and typed Go/Java/C# code face breakage. The old version still works with no sunset date, yet new features will likely land only on the new one.

4. Caveat: mixing old Bedrock models with new SDKs will not work.