Claude change history: Intermittent error spikes for Claude Mythos 5.1 and Claude Fable 5.1

Claude reported major intermittent errors for Claude Mythos 5.1 and Claude Fable 5.1 affecting claude.ai, Claude API (api.anthropic.com), Claude Code and Claude Cowork. The incident ran from 2026-09-15 09:48 UTC to 2026-09-15 11:14 UTC, lasting 1 h 26 min. A fix was deployed at 10:50 UTC, followed by monitoring and resolution.