# Anthropic: Elevated errors for Claude Mythos 5.1 and Claude Fable 5.1

- Impact (vendor’s label): major
- Status: resolved
- Started: 2026-09-11 14:19 UTC · Resolved: 2026-09-11 14:37 UTC · Duration: 17 min
- Updates: 5 · Affected components: Claude Cowork, Claude API (api.anthropic.com), claude.ai, Claude Code
- [Vendor status page: https://stspg.io/n9n8kfcxtkfm](https://stspg.io/n9n8kfcxtkfm)
- [Company: Anthropic](https://rewindex.com/company/anthropic.md)

## 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, sol)_
## Timeline of updates

- **investigating** 2026-09-11 14:19 UTC: 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.
- **identified** 2026-09-11 14:21 UTC: 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.
- **monitoring** 2026-09-11 14:28 UTC: A fix has been deployed for Claude Mythos 5.1 and Claude Fable 5.1 and we are monitoring for recovery.
- **monitoring** 2026-09-11 14:28 UTC: A fix has been deployed for the issue affecting Claude services and we are monitoring for recovery.
- **resolved** 2026-09-11 14:37 UTC: The issue affecting Claude services has been resolved. Impact occurred from 13:57 to 14:20 UTC

## Rewindex changes for this incident

- 2026-09-11 14:19 UTC: [Major incident: Elevated errors for Claude Mythos 5.1 and Claude Fable 5.1](https://rewindex.com/change/i055b3888ce3932.md)


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Canonical: https://rewindex.com/company/anthropic/incidents/t33dncr5ydvl · Markdown: https://rewindex.com/company/anthropic/incidents/t33dncr5ydvl.md · JSON: https://rewindex.com/api/v1/companies/anthropic/incidents/t33dncr5ydvl · Generated 2026-10-18T11:45:01.616Z