Microsoft's two-day outage took Claude and ChatGPT down with it

A Microsoft outage left millions of people worldwide unable to use Outlook, Teams and other Microsoft 365 tools from Thursday into a second day on Friday, and the disruption spread to the AI assistants many of those users rely on to handle their work email and calendars 3

3

2

2

.

Why the AI assistants went down

Microsoft ruled out malicious activity and said the outage was caused by server overload 2

2

1

1

. Claude and ChatGPT do not just chat; when the integrations work, they can summarize email threads, pull out action items, draft replies and check calendars. When they fail, business users may have to handle email, supplier dates and meeting coordination by hand 1

1

.

On November 12 and 13, both Anthropic's Claude and OpenAI's ChatGPT reported disruptions to their Microsoft 365 integrations, with authentication problems and failing mail, calendar and search requests. Neither lab said how many users were affected 2

2

1

1

.

Anthropic said its connector problems were down to the Microsoft incident, and that most requests across mail, calendar and search were failing, with Claude for Outlook hit too. On November 12 it said it was working with Microsoft as the upstream provider restarted affected servers, with a complete resolution still pending 3

3

1

1

.

The two assistants were not equally exposed. Claude reaches mail, calendar, Teams chats and SharePoint files through one Microsoft 365 connector; ChatGPT connects to Outlook email and calendar through separate plugins. Because Claude reaches all of those through a single connector, a failure there cut off the whole set at once, while ChatGPT's separate plugins limited its exposure. OpenAI described its tools as not working as expected 1

1

.

A second, separate failure at Anthropic

Claude had a problem of its own. On Friday morning, Anthropic posted that it was investigating users who could not get into Claude.ai and Claude Code. Its status page listed claude.ai as a major outage, Claude Code and the developer console as partial outages, and the Claude API as still operational. "A fix has been deployed for the issue affecting Claude services and we are monitoring for recovery. We are investigating an issue with users authenticating to Claude.ai and Claude Code. We will provide an update as soon as possible," the status page said 3

3

.

The user impact showed up in complaint volumes. Downdetector recorded 2,895 Claude outage reports at around 3:45 PM on Friday, against a baseline of about two. The figure counts complaints rather than affected users 3

3

.

Both companies showed signs of recovery by late Friday morning, though some SharePoint searches were still returning errors 1

1

. As of Friday, Anthropic had not said what was behind the login problem or when it expected to fix it 3

3

.