Claude

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Elevated errors for Claude Mythos 5.1 and Claude Fable 5.1

Updated 11 Sep 2026, 16:40 UTC

Resolved 14:21Started 2Timeline events

Confirmed by the official source.

Executive summary

Summary
Claude officially reported elevated errors affecting requests to Claude Mythos 5.1 and Claude Fable 5.1. A fix was deployed, and recovery is being monitored; Claude Cowork remained in partial outage in the latest status update.

What users experienced

User impact
Requests to Claude Mythos 5.1 and Claude Fable 5.1 experienced elevated errors. Claude reported partial outages across claude.ai, the Claude API, Claude Code, and Claude Cowork during the incident.

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Started

14:2111 Sep 2026

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Timeline events

Timeline of the incident

11 Sep 2026, 14:22 UTC
Detection
Confirmed by an official service source.
11 Sep 2026, 16:40 UTC
Resolution
The service is no longer reporting this incident as active.

What we know

✓Claude began investigating elevated errors at 14:19:51 UTC.
✓Claude identified the affected requests as those for Mythos 5.1 and Fable 5.1.
✓The provider deployed a fix and moved the incident to monitoring.
✓The latest status listed claude.ai, the Claude API, and Claude Code as operational, with Claude Cowork still in partial outage.