Anthropic resolved an incident of elevated errors affecting Claude Fable 5 and 5.1, Mythos 5 and 5.1, and Claude Opus 5. The issue occurred from 5:50pm PT to 7:10pm PT on September 22, 2026. Success rates returned to normal for Fable 5, 5.1 and Mythos 5, 5.1, while Opus 5 remained under repair.

The incident impacted claude.ai, Claude API (api.anthropic.com), Claude Code, and Claude Cowork.