EVENT DOSSIER
On Thursday, September 3, 2026, at noon, cloud-based artificial intelligence models operated by OpenAI, Anthropic, xAI, and Google experienced a rare and significant simultaneous service outage. Anthropic was the first to report partial downtime due to a high error rate in requests related to Claude Mythos 5.1 and Claude Fab. Subsequently, the main AI services of the other three companies were also affected, resulting in all four companies experiencing service failures at the same time.
# Four major AI models suffer rare overlapping downtime Cloud-based AI models operated by OpenAI, Anthropic, xAI, and Google experienced a rare and overlapping set of significant service interruptions over a period of hours Thursday morning. Anthropic first reported a "partial outage" related to "elevated errors on requests to Claude Mythos 5.1, Claude Fab…