Errors hit Claude Sonnet 5, Haiku 4.5 and Claude Code

Anthropic is investigating elevated errors on requests to Claude Mythos 5, Claude Fable 5, Claude Opus 5, Claude Sonnet 5, Claude Haiku 4.5 and other models, with two notices posted at 16:20 UTC on Aug 18. Both entries appeared on the Claude status page within the same minute.

At a glance

• The incident spans claude.ai, the Claude API at api.anthropic.com, Claude Code and Claude Cowork, meaning both the subscription apps and programmatic access are covered by the same investigation.
• Two similar multi-model degradations preceded it this month: the Aug 5 outage ran 7 hours 8 minutes with a peak of 85 user reports per hour, the Aug 12 one 4 hours 16 minutes.
• It is the third multi-model degradation in two weeks, and so far Anthropic has published neither a cause nor a restoration estimate for the Aug 18 incident.

For teams routing production traffic through api.anthropic.com, a third degradation inside two weeks reads as a reliability pattern rather than an isolated fault, and the placement of Claude Code and Claude Cowork inside the same incident means editor workflows and hosted sessions degrade together with app traffic. With no cause named, the practical question is duration, and the August precedents ran in hours rather than minutes.

The incident opened with a short investigating notice about reports of degraded performance across multiple models. A second entry, posted at the same timestamp, reframed it as elevated errors on requests and listed the models involved. Anthropic said it would provide an update as soon as possible.

The Aug 5 degradation, also described as affecting multiple models, lasted 7 hours 8 minutes and peaked at 85 user reports per hour. The Aug 12 incident ran 4 hours 16 minutes with a peak of two reports per hour, a far smaller spike for a comparable window. Both were resolved.

The list spans the current lineup rather than a single tier: Claude Mythos 5, Claude Fable 5, Claude Opus 5 and Claude Sonnet 5 sit alongside Claude Haiku 4.5, the only model named from an earlier generation, with the notice extending to other Claude models beyond those five.

No cause, no ETA

Anthropic has not published a cause for the Aug 18 errors and has set no restoration estimate; the status entry commits only to a further update as soon as possible. The status page does not connect the earlier August degradations to the current one, and the incident remains open across all four affected surfaces.