Funny, I went to their status page before coming here, and it definitely was "all systems go."
> June 05, 2017 21:00 CEST Minor service outage.
> June 05, 2017 21:10 CEST Major service outage.
> June 05, 2017 21:21 CEST GitHub.com is recovering, we are continuing to monitor.
> June 05, 2017 21:31 CEST Everything operating normally.
> June 06, 2017 00:00 CEST All systems reporting at 100%
> June 07, 2017 01:19 CEST Major service outage.
Like you said, they went from 100% to major service outage.