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

Claude 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 at 2026-10-05 13:05 UTC and resolved at 2026-10-05 13:21 UTC (computed duration: 15 min); the vendor separately stated an impact window of 12:40 UTC to 13:10 UTC.