LLM model/API behavior drift

Anthropic Claude API output_format output_config format structured output

Structured-output requests return a validation error after model migration.

Claude APIHosted AI APIsLLM model/API behavior driftanthropic_migrate

Agent Quick Fix

Repair against the current Claude API contract, then keep the change narrow and source-backed.

Product: Claude API
Current-contract area: Old beta `output_format` field moved under `output_config.format`
Likely root cause: Structured-output requests return a validation error after model migration.
Repair direction: Verifier checks current model ID, accepted payload, structured output/tool parsing, and behavior under retries.

Symptom

Structured-output requests return a validation error after model migration.

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.

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 structured outputs output_format output_config format beta
Anthropic Claude API output_format output_config format structured output
output_format site:docs.anthropic.com/en/api/messages
site:docs.anthropic.com/en/docs "structured outputs" "Claude"
https://docs.anthropic.com/en/api/messages
"output_config" "format" "Claude"
"output_config" "output_format" "API"