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

Anthropic reported a major incident with 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. It started 2026-10-05 13:05 UTC and resolved at 2026-10-05 13:21 UTC (computed duration: 15 min); the vendor reported impact from 12:40 UTC to 13:10 UTC.