Chi Wang(@Chi_Wang_):Anthropic confirmed Claude went down around 9:41 AM ET, with Mythos, Fable, and Opus all affected. The Verge reports ChatGPT and Grok went down in the same window. Most agent stacks treat model fallback as the reliability plan: retry, then drop to a cheaper model. This outage took out every model behind one API, so the failure was in the serving layer, not the model. A fallback list inside one provider is one dependency with extra names. What survives is state kept outside the provider session, so an agent can resume instead of restart.

2026.09.03 18:00

Anthropic confirmed Claude went down around 9:41 AM ET, with Mythos, Fable, and Opus all affected. The Verge reports ChatGPT and Grok went down in the same window. Most agent stacks treat model fallback as the reliability plan: retry, then drop to a cheaper model. This outage took out every model behind one API, so the failure was in the serving layer, not the model. A fallback list inside one provider is one dependency with extra names. What survives is state kept outside the provider session, so an agent can resume instead of restart.