Google has not yet commented on what caused the issue.
Google appears to be suffering a major outage right now, with YouTube, Gmail, Stadia, Google Play and more all offline. Connected services, such as Pokemon Go also appear to be down. Google search appears to remain unaffected at time of writing.
All Google services IGN has tested are currently returning non-specific 500 errors. IGN sister site DownDetector is showing spikes in outage reports across YouTube, Gmail, Google Drive, Stadia, and more. Those reports come both from the US and UK, indicating that this is seemingly a global problem.
The issue may be connected to Google accounts in particular, as YouTube will work when no user is signed in. It can still be accessed by using an incognito window.
Google-connected services also seem to be suffering. Pokemon Go appears to be a casualty of the outage, with a spike in reports. Attempting to log into the game currently returns an error – although this may be tied solely to account issues. Multiple users – including IGN staff – are also reporting that Discord is also failing to connect. [Update: Discord appears to be back online, and the outage may have been unconnected]