# AN-2026-0002: Claude Haiku 5.5 (claude-haiku-5-5) released, with migration gotchas for Haiku 4.5 code

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- id: AN-2026-0002 (version 1; cite https://breakwire.org/claim/AN-2026-0002/v/1)
- kind: release · status: active · review: editor
- source: <https://www.anthropic.com/claude-haiku-5-5>
- more sources: <https://platform.claude.com/docs/en/release-notes/overview>
- event date: 2026-10-07
- services: anthropic-api
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 3, fixed 0, not fixed 0

## Summary
```text
Migration details are in the Claude Platform release notes for October 7, 2026: https://platform.claude.com/docs/en/release-notes/overview
```

## Statements (checkable)
0. Anthropic says Haiku 5.5 costs around 75% less to run than Haiku 4.5 on average.  [✓0 ✗0]
1. Release notes: 1M token context window, 128k max output tokens, adaptive thinking with the effort parameter.  [✓0 ✗0]
2. Release notes: on Haiku 5.5, budget_tokens, temperature/top_p/top_k and assistant prefill can each return 400; computer_20250124 returns 400 (use computer_toolset_20260801 on the Claude API and Google Cloud).  [✓0 ✗0]
3. Adaptive thinking is on by default; thinking text is omitted unless thinking.display is set to "summarized".  [✓0 ✗0]
4. Same day: Claude Sonnet 5.5 prompt cache reads cut from $0.20 to $0.10 per million tokens.  [✓0 ✗0]

## Fix
```text
If you swap claude-haiku-4-5 for claude-haiku-5-5 as a subagent model, strip sampling params, budget_tokens and assistant prefill first, and expect responses that may start with thinking blocks.
```

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0002/reports_

## History
- v1 2026-10-28 by wire-editor: migrated from v0.1 post #2