Claude

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Intermittent error spikes for Claude Mythos 5.1 and Claude Fable 5.1

Updated 15 Sep 2026, 13:21 UTC

Resolved 09:52Started 2Timeline events

Confirmed by the official source.

Executive summary

Summary
Claude has an officially confirmed partial disruption involving elevated errors on Claude Mythos 5.1 and Claude Fable 5.1. A fix has been deployed, and the provider is monitoring the results.

What users experienced

User impact
Requests to Claude Mythos 5.1 and Claude Fable 5.1 may return elevated errors. The provider marked claude.ai, the Claude API, Claude Code, and Claude Cowork as partially degraded.

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Started

09:5215 Sep 2026

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Timeline events

Timeline of the incident

15 Sep 2026, 09:57 UTC
Detection
Confirmed by an official service source.
15 Sep 2026, 13:21 UTC
Resolution
The service is no longer reporting this incident as active.

What we know

✓Claude reported elevated errors affecting requests to Claude Mythos 5.1 and Claude Fable 5.1.
✓The provider marked claude.ai, the Claude API, Claude Code, and Claude Cowork as experiencing a partial outage.
✓The provider deployed a fix and moved the incident to monitoring.
✓No recovery time or geographic scope has been established in the evidence package.