Claude API version 2026-10-21 drops temperature

Anthropic published a migration guide for Claude API version 2026-10-21. Under the new version, “a request that sends temperature, top_p, or top_k returns a 400 error, even at the parameter’s default value.” Requests without those settings sample with the defaults, including a temperature of 1.0.

The guide is direct about the effect. On models that accept other values, “a request that lowered temperature for more consistent output loses that effect. No other setting replaces it.” Integrations that need a non-default value can stay on the older version, 2023-06-01. SDK releases default to the version that was current when their major version shipped, so a routine SDK upgrade can carry a vendor onto the new behavior.

Many vendors lower temperature to make classification, extraction and summarization repeatable. A validated model whose sampling changes is a changed model for model-risk purposes.

What this means for your bank

Ask vendors whose controls run on Claude which API version they call and whether they relied on a low temperature.
Treat a move to version 2026-10-21 as a model change that needs revalidation of outputs your controls depend on.

Sources

Migrating to API version 2026-10-21 (Claude Docs)platform.claude.com ↗

This is for information only and is not legal advice. Confirm the behavior of your vendors’ integrations directly with them.

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