Over the last 90 days the status page (https://www.githubstatus.com/) shows around 2 nines of uptime for most services.
The Missing GitHub Status Page (https://mrshu.github.io/github-statuses/) gives a better overview of their frequent outages.
loading story #48283556
at least enterprise is better https://us.githubstatus.com/posts/dashboard
I trust that about as much as I trust Volkswagen's emissions numbers.