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Claude API 400 error after an SDK update? temperature, top_p and top_k are gone

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Source checked 2 Nov 2026 · Published 2 Nov 2026 · Last reviewed 2 Nov 2026 · By Ctrl+Z Therapy (how we test)

The short answer

Anthropic released API version 2026-10-21 on October 21, 2026, and new SDK versions send it by default: Python SDK 2.0.0 (the anthropic package) and TypeScript SDK 1.0.0 (@anthropic-ai/sdk). In 2026-10-21, a request that sends temperature, top_p, or top_k returns a 400 error, even at the parameter's default value. The new SDKs and the CLI no longer have the three parameters, so remove them from your requests.

What to do

  1. Check which SDK version your app uses. If you use an SDK, your requests use the API version that was current when your SDK's major version was released.
  2. Remove temperature, top_p and top_k from every Claude request in your code.
  3. Go through the other breaking changes in Anthropic's migration guide, then test against the new version before you release.

Good to know

  • Models that already accept only the defaults, such as Claude 4.7 and later models, sample as before.
  • On models that accept other values, such as Claude Sonnet 4.6, a request that lowered temperature for more consistent output loses that effect, and no other setting replaces it.
  • The new SDKs also send your API key as Authorization: Bearer. If a proxy or gateway in front of your app reads the old X-Api-Key header, update it too.

Source

Checked on 2 Nov 2026. Prices, limits and settings change, so check the source before you rely on them.

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