Anthropic: Intermittent error spikes for Claude Mythos 5.1 and Claude Fable 5.1

Impact: majorStatus: resolvedStarted 2026-09-15 09:48 UTCResolved 2026-09-15 11:14 UTC (1.4 h)4 updatesSource: stspg.io

Summary

Anthropic reported major intermittent error spikes 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 started at 2026-09-15 09:48 UTC and was resolved at 2026-09-15 11:14 UTC, lasting 1 h 26 min; a fix was deployed by 10:50 UTC.

Machine-written from the archived incident (Sol). Check the timeline before relying on it.

Affected components: Claude CoworkClaude API (api.anthropic.com)claude.aiClaude Code

Timeline of updates

investigating2026-09-15 09:48 UTC
We are investigating elevated errors on requests to Claude Mythos 5.1 and Claude Fable 5.1. We will provide an update as soon as possible.
investigating2026-09-15 09:52 UTC
We are investigating elevated errors on requests to Claude Mythos 5.1 and Claude Fable 5.1. We will provide an update as soon as possible.
monitoring2026-09-15 10:50 UTC
A fix has been deployed for Claude Mythos 5.1 and Claude Fable 5.1 and we are monitoring to ensure it has resolved the issue.
resolved2026-09-15 11:14 UTC
A fix has been deployed for Claude Mythos 5.1 and Claude Fable 5.1 and we are monitoring to ensure it has resolved the issue.

Rewindex changes for this incident

Major incident: Intermittent error spikes for Claude Mythos 5.1 and Claude Fable 5.1 2026-09-15 09:48 UTC

Impact, status and times are the vendor’s own, as last archived. View on stspg.io (opens in new tab). Anthropic profile · Recent Anthropic incidents · Markdown · JSON