GitDocs
LLM model/API behavior drift

Anthropic "thinking" "disabled" "Claude" API

Latency-sensitive code receives a 400 despite the SDK accepting the field.

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: `thinking: disabled` rejected by always-on adaptive-thinking model
Likely root cause: Latency-sensitive code receives a 400 despite the SDK accepting the field.
Repair direction: Verifier checks current model ID, accepted payload, structured output/tool parsing, and behavior under retries.

Symptom

Latency-sensitive code receives a 400 despite the SDK accepting the field.

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 latency 400 SDK accepts field service_tier latency_sensitive
site:docs.anthropic.com/en/docs Claude API thinking disabled 400 adaptive thinking model
Anthropic "thinking" "disabled" "Claude" API
Anthropic docs extended thinking API
site:docs.anthropic.com "adaptive thinking" Claude API
docs.anthropic.com claude api adaptive thinking effort levels
https://docs.anthropic.com/en/api/messages
https://platform.claude.com/docs/llms.txt
site:anthropic.com/news "adaptive thinking" "disabled"
"Claude Opus 4.6: Adaptive thinking and 1M context window"
github anthropics anthropic-sdk-typescript thinking disabled adaptive thinking
github.com anthropics anthropic-sdk-typescript "type": "disabled" "thinking"
https://raw.githubusercontent.com/anthropics/anthropic-sdk-typescript/main/src/resources/messages/messages.ts
'ThinkingConfig' in https://raw.githubusercontent.com/anthropics/anthropic-sdk-typescript/main/src/resources/messages/messages.ts
https://platform.claude.com/docs/en/build-with-claude/adaptive-thinking

Source Trail

GitHub source file/reference: