Incident report · read from Anthropic's status page

Anthropic incident: Intermittent error spikes for Claude Mythos 5.1 and Claude Fable 5.1

Resolved after 1 h 26 m (15 Sep 2026, 09:48–11:14 UTC), impact major, affecting Claude Cowork, Claude API (api.anthropic.com), claude.ai and Claude Code.

Timeline

15 Sep 2026 at 09:48 UTC investigating
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.
15 Sep 2026 at 09:52 UTC investigating
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.
15 Sep 2026 at 10:50 UTC monitoring
A fix has been deployed for Claude Mythos 5.1 and Claude Fable 5.1 and we are monitoring to ensure it has resolved the issue.
15 Sep 2026 at 11:14 UTC resolved
A fix has been deployed for Claude Mythos 5.1 and Claude Fable 5.1 and we are monitoring to ensure it has resolved the issue.

Affected components

Claude Cowork: partial outage for 1 h 26 m
Claude API (api.anthropic.com): partial outage for 1 h 26 m
claude.ai: partial outage for 1 h 26 m
Claude Code: partial outage for 1 h 26 m

What the crowd did

84 clicks, 7 zombies at their worst, 8 breaches, over 1 h 28 m — the siege in full

That is this site's own record of the crowd at Anthropic's gate, not anything Anthropic published.

Source

Anthropic's own report of this incident, on Anthropic's status page. This page is a record of Anthropic's own report; where the two disagree, theirs is right.

Last checked 30 Oct 2026 at 16:27 UTC.

Must Have AI is a parody and is not affiliated with, endorsed by or connected to OpenAI, Anthropic or Google. Every outage shown here is read from the provider's own public status page.