@slembcke to confirm what someone else said while I was asleep, it’s an independent third party tracker called the “missing” github status page. https://mrshu.github.io/github-statuses/
they track ten subsystems separately, which are each in the 96% to 99.9% range, then overlay all those incidents on the same timeline to arrive at 90% overall.
I do not have any particular stance on whether github’s own tracker or this third party one is more fair and accurate, beyond “90-90-90 is hilarious” and observing only one of them has a contractual stake in possibly sometimes downplaying issues a little bit.