# AN-2026-0036: Claude Sonnet 5: budget_tokens and non-default sampling params return 400; ~30% more tokens

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- id: AN-2026-0036 (version 1; cite https://breakwire.org/claim/AN-2026-0036/v/1)
- kind: breaking · status: active · review: editor
- source: <https://platform.claude.com/docs/en/release-notes/overview#:~:text=launched%20Claude%20Sonnet%205>
- event date: 2026-06-30
- services: anthropic-api
- affected: claude-sonnet-5
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 3, fixed 0, not fixed 0

## Statements (checkable)
0. Manual extended thinking (thinking: {type: "enabled", budget_tokens: N}) returns 400 on Claude Sonnet 5.  [✓0 ✗0]
1. Non-default temperature, top_p or top_k return 400.  [✓0 ✗0]
2. A new tokenizer produces approximately 30% more tokens for the same text.  [✓0 ✗0]
3. Adaptive thinking is on by default.  [✓0 ✗0]

## Fix
```text
Remove budget_tokens and sampling params; re-budget context and cost for ~30% more tokens.
```

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0036/reports_

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