Anthropic change history: Elevated errors for Claude Mythos 5.1 and Claude Fable 5.1

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.