# Claude: Major incident: Elevated errors for Claude Mythos 5.1 and Claude Fable 5.1

**Summary:** Claude reported major elevated errors for Claude Mythos 5.1 and Claude Fable 5.1 across claude.ai, Claude API (api.anthropic.com), Claude Code and Claude Cowork. The incident started at 2026-10-05 13:05 UTC and resolved at 2026-10-05 13:21 UTC (computed duration: 15 min); the vendor separately stated an impact window of 12:40 UTC to 13:10 UTC. _(machine-written, sol)_
- Kind: Major incident · Label: outage (model (Jev))
- Changed: 2026-10-05 13:05 UTC · Detected: 2026-10-17 18:22 UTC
- [Source: https://stspg.io/wdqhxt8xt574](https://stspg.io/wdqhxt8xt574)
- [Company: Claude](https://rewindex.com/company/claude.md)
- Versions: before (none: first archived) → after incident\_version:6/bhphxz3vr58g@a011bba09e6d
- Change 1 of 1 for this incident

## What changed

**1. Added: Title**

```diff
+ Elevated errors for Claude Mythos 5.1 and Claude Fable 5.1
```

**2. Added: Impact**

```diff
+ major
```

**3. Added: Status**

```diff
+ resolved
```

**4. Added: Start time**

```diff
+ 2026-10-05 13:05 UTC
```

**5. Added: Resolved time**

```diff
+ 2026-10-05 13:21 UTC
```

**6. Added: Affected components**

```diff
+ claude.ai, Claude API (api.anthropic.com), Claude Code, Claude Cowork
```

**7. Added: Update** (investigating) · 2026-10-05 13:05 UTC

```diff
+ We are investigating elevated errors on requests to Claude Mythos 5.1 and Claude Fable 5.1. We will provide an update as soon as possible.
```

**8. Added: Update** (resolved) · 2026-10-05 13:21 UTC

```diff
+ The issue affecting Claude Mythos 5.1 and Claude Fable 5.1 has been resolved. Impact occurred from 05:40 PT / 12:40 UTC to 06:10 PT / 13:10 UTC.
```

## History of this incident

| When (UTC) | Change | Label |
| --- | --- | --- |
| 2026-10-05 13:05 UTC | Major incident: Elevated errors for Claude Mythos 5.1 and Claude Fable 5.1 (this change) | outage |

All Claude changes: [timeline](https://rewindex.com/company/claude/changes.md)
_Diff excerpts are shown on normalized text: dates, counters and tokens appear as ‹date›, ‹count›, ‹tok›; noise-only edits are hidden. Rewindex shows the changed passages, not a copy of the page._


---
Canonical: https://rewindex.com/change/i9e2e08048ef594 · Markdown: https://rewindex.com/change/i9e2e08048ef594.md · JSON: https://rewindex.com/api/v1/changes/i9e2e08048ef594 · Generated 2026-10-18T01:29:46.132Z