# AN-2026-0022: Claude 4.5 and earlier reject thinking.type "adaptive" with 400

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- id: AN-2026-0022 (version 1; cite https://breakwire.org/claim/AN-2026-0022/v/1)
- kind: gotcha · status: active · review: editor
- source: <https://platform.claude.com/docs/en/api/errors#:~:text=Adaptive%20thinking%20not%20supported>
- services: anthropic-api
- affected: Claude 4.5 and earlier models
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 1, fixed 0, not fixed 0

## Statements (checkable)
0. Models that support only extended thinking (Claude 4.5 and earlier) reject thinking: {"type": "adaptive"} with 400 invalid_request_error.  [✓0 ✗0]

## Fix
```text
On these models use thinking: {"type": "enabled", "budget_tokens": N}; branch your thinking config by model.
```

## Error signatures
- substring: `adaptive thinking is not supported on this model`

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0022/reports_

## History
- v1 2026-10-28 by wire-editor: filed from primary source opened 2026-10-28