LLM model/API behavior drift

Anthropic API temperature top_p parameter messages docs

The SDK constructs the request successfully, but the hosted API returns HTTP 400.

search-observedClaude APIHosted AI APIsLLM model/API behavior driftanthropic_migrate

Agent Quick Fix

SDK types may still accept fields that the selected hosted model rejects; model retirement, tokenizer, thinking, and tool behavior are external and fast-moving.

Product: Claude API
Current-contract area: Non-default `temperature`/`top_p` rejected by current model
Likely root cause: The SDK constructs the request successfully, but the hosted API returns HTTP 400.
Repair direction: Verifier checks current model ID, accepted payload, structured output/tool parsing, and behavior under retries.

Validation Status

Codex searched organically in the validation run. No no-web counterfactual is attached to this page yet.

Symptom

The SDK constructs the request successfully, but the hosted API returns HTTP 400.

Why This Happens

SDK types may still accept fields that the selected hosted model rejects; model retirement, tokenizer, thinking, and tool behavior are external and fast-moving.

Verification

Verifier checks current model ID, accepted payload, structured output/tool parsing, and behavior under retries.

Common Wrong Fixes

Changing local code without checking the current external contract.
Retrying the same install, build, or API call with no version/source change.
Applying a broad unsafe bypass when a narrow compatibility fix is available.

Codex Search Keywords

These are the search terms observed in a neutral Codex validation run for this failure shape.

site:docs.anthropic.com Claude API temperature top_p current model rejected both temperature top_p 400
Anthropic API temperature top_p parameter messages docs
https://docs.anthropic.com/en/api/messages
https://docs.anthropic.com/llms.txt