Anthropic confirmed a partial outage across its Claude platform on Tuesday, September 29, after a disruption began shortly before 10:00 a.m. ET. Elevated error rates affected Claude.ai — including the desktop and mobile apps — along with Claude Code, Claude Cowork, and eventually the Claude API, with users seeing failed requests, error-loading conversations, and forced sign-in loops. Downdetector recorded over 18,000 problem reports at peak, with reports concentrated in the US and India.

Anthropic opened an incident on its status page at 14:21 UTC, applied a partial mitigation at 14:41 UTC, then hit a second failure that took out single sign-on, Sign in with Apple, new chats, voice conversations, purchases and file uploads. By 14:59 UTC (10:59 a.m. ET) the company said all services were operating normally — roughly an hour after the 14:00 UTC start — and the incident moved to monitoring at 15:11 UTC. Anthropic warned that some messages sent between 14:00 and 14:59 UTC may not have been saved, and never disclosed a root cause. Signed-in users were told not to log out, to avoid authentication loops.

It was the 13th incident logged on Anthropic's status page this month, with September uptime at 99.70%, per Unite.ai. Spotify suffered its own outage at the same time — Downdetector reports peaking above 19,000 — though there is no sign the two were linked. 9to5Google noted limited, inaccurate reports of ChatGPT and Gemini being down too; neither OpenAI nor Google confirmed issues.

The timing is awkward: the outage landed one day after Anthropic released Claude Sonnet 5.5, and on the same morning as OpenAI's DevDay keynote — a day when the frontier labs were hoping to look their most reliable.