Anthropic / breaking change
Newer Claude models restrict or reject explicit sampling parameters
For models released after Claude Opus 4.6, Anthropic accepts temperature only at 1.0 and top_p only at 0.99 or higher, while any explicit top_k is rejected with HTTP 400. The Python SDK version 1.0 and later rejects these fields locally with TypeError.
- Affected product / version
- Claude Messages API; models released after Opus 4.6
- Announced
- Not specified in cited documentation
- Effective
- Not specified in cited documentation
- Source checked
Checked against the linked documentation on 2026-09-07. Recheck the vendor documentation before acting.
What to check in your application
PlaintextML interpretation of the documented change:
- Remove explicit sampling controls from shared Claude request builders before changing a model identifier to Opus 4.7 or later, including configuration defaults added by wrappers.
- Replace sampling-based behavior tuning with prompts, and add a migration test that exercises the exact production payload against the target model rather than relying only on static SDK types.
Limits and uncertainty
The API reference describes models released after Opus 4.6; the deprecations table names Opus 4.7 and later plus Mythos Preview. Neither supplies a single enforcement date. Omit these fields rather than assuming all model and SDK combinations accept the same exceptions.
Official sources
Revision history
- — Initial record added after checking the linked official documentation; migration checks are editorial interpretation.
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