Overview
- Anthropic logged elevated authentication errors around 09:58 UTC on Friday that blocked logins to claude.ai, Claude Code and platform.claude.com and forced status updates as engineers investigated.
- The company reported two separate incidents that day, saying it deployed a fix for the first outage late morning and later resolved a broader degraded-performance incident in the afternoon.
- Anthropic identified a concurrent Microsoft 365 service incident as the cause of failures in its Microsoft 365 connector, which produced mail, calendar and search errors inside Claude integrations.
- Service impact was uneven: the Claude web chat and coworking surfaces showed major or degraded outages for many users while the Claude API, Code and Console were reported operational in status updates.
- Users in the US, India and the UK reported login failures, unexpected logouts, expired OAuth sessions and credential-precedence errors, and the company’s investigation comes against a backdrop of earlier 2026 authentication and session-token incidents.