Updated 10:35 p.m. Eastern on September 21, 2026
Claude reports elevated errors for multiple models, with the incident now resolved according to the latest official update. Impact occurred from 5:50pm PT / 00:50 UTC to 7:10pm PT / 02:10 UTC.
What is affected
The incident affected requests to Claude Mythos 5.1, Claude Fable 5.1, and Claude Opus 5, with impact across claude.ai, Claude API, Claude Code, and Claude Cowork.
Official update timeline
We are investigating elevated errors on requests to Claude Mythos 5.1, Claude Fable 5.1, and Claude Opus 5. We will provide an update as soon as possible.
We have identified the cause of elevated errors on requests to Claude Mythos 5.1, Claude Fable 5.1, and Claude Opus 5 and are working on a fix. We will provide an update as soon as possible.
We are continuing to work to resolve errors affecting some models. At this time, requests to Claude Fable 5 and 5.1 and Mythos 5 and 5.1 have returned to normal success rates. We are working to resolve remaining errors affecting Claude Opus 5, and will provide an additional update shortly.
We have seen success rates return to normal across affected models, and are monitoring closely to ensure no further issues.
This issue has been resolved. Impact occurred from 5:50pm PT / 00:50 UTC to 7:10pm PT / 02:10 UTC.
