Changes / Anthropic / Elevated errors for Claude Mythos 5.1 and Claude Fable 5.1

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

Summary

Anthropic 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 2026-09-11 14:19 UTC, lasted 17 min and was resolved after a fix was deployed; Anthropic separately reported impact from 13:57 to 14:20 UTC.

Machine-written from the diff below (Sol; type: incident outage). Check the diff before relying on it.

Major incidentLabel: outage (model (Jev), 96%)Changed Detected Source: stspg.io

What changed

AddedTitle#1
Before: not present
After: Elevated errors for Claude Mythos 5.1 and Claude Fable 5.1
AddedImpact#2
Before: not present
After: major
AddedStatus#3
Before: not present
After: resolved
AddedStart time#4
Before: not present
After: 2026-09-11 14:19 UTC
AddedResolved time#5
Before: not present
After: 2026-09-11 14:37 UTC
AddedAffected components#6
Before: not present
After: claude.ai, Claude API (api.anthropic.com), Claude Code, Claude Cowork
AddedUpdateinvestigating#7
Before: not present
After: We are investigating elevated errors on requests to Claude Fable 5.1 and Claude Mythos 5.1. We will provide an update as soon as possible.
AddedUpdateidentified#8
Before: not present
After: We have identified the cause of elevated errors on requests to Claude Mythos 5.1 and Claude Fable 5.1 and are working on a fix. We will provide an update as soon as possible.
AddedUpdatemonitoring#9
Before: not present
After: A fix has been deployed for Claude Mythos 5.1 and Claude Fable 5.1 and we are monitoring for recovery.
AddedUpdatemonitoring#10
Before: not present
After: A fix has been deployed for the issue affecting Claude services and we are monitoring for recovery.
AddedUpdateresolved#11
Before: not present
After: The issue affecting Claude services has been resolved. Impact occurred from 13:57 to 14:20 UTC

First version of this incident archived by Rewindex. View the live incident.

History of this incident

When (UTC)ChangeKind
Major incident: Elevated errors for Claude Mythos 5.1 and Claude Fable 5.1 (this change)
Anthropic 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 2026-09-11 14:19 UTC, lasted 17 min and was resolved after a fix was deployed; Anthropic separately reported impact from 13:57 to 14:20 UTC.
Major incident

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