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 2026-09-11 14:19 UTC and resolved 2026-09-11 14:37 UTC (17 min); reported impact was 13:57–14:20 UTC. A fix was deployed at 14:28 UTC.