# AN-2026-0688: Anthropic deprecates fast mode for Claude Opus 4.8: removal Nov 30, 2026, after which claude-opus-4-8 requests with speed "fast" return an error

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- id: AN-2026-0688 (version 2; cite https://breakwire.org/claim/AN-2026-0688/v/2)
- kind: deprecation · status: active · review: editor
- source: <https://platform.claude.com/docs/en/release-notes/overview#:~:text=deprecated%20fast%20mode%20for%20Claude%20Opus%204.8>
- more sources: <https://platform.claude.com/docs/en/build-with-claude/fast-mode#supported-models>
- event date: 2026-10-30
- services: anthropic-api
- affected: claude-opus-4-8; claude-opus-4-8 with speed: "fast"; fast-mode-2026-02-01
- ACT BY: 2026-11-30
- severity: medium
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. Anthropic's Claude Platform release notes for October 30, 2026 (opened 2026-11-03) say fast mode is deprecated for Claude Opus 4.8, with removal on November 30, 2026.  [✓0 ✗0]
1. After removal, requests to claude-opus-4-8 with speed: "fast" will return an error; to keep using fast mode Anthropic says to migrate to Claude Opus 5.5.  [✓0 ✗0]
2. The fast mode docs (opened 2026-11-03) list fast mode on Claude Opus 5 and Claude Opus 4.8 as research preview needing the fast-mode-2026-02-01 beta header, while Claude Opus 5.5 fast mode no longer needs the header.  [✓0 ✗0]

## Fix
```text
Before Nov 30, 2026 move fast-mode traffic from claude-opus-4-8 to claude-opus-5-5 (see the Opus 5.5 migration guide section on migrating from Claude Opus 4.8); after removal, claude-opus-4-8 requests that still send speed: "fast" error.
```

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0688/reports_

## History
- v2 2026-11-03 by wire-editor: affected: add bare model id claude-opus-4-8 so model-id matching applies (same source, release notes 2026-10-30) (changed affected)
- v1 2026-11-03 by wire-editor: promoted from candidate #142 (anthropic-release-notes) after review