good: ~99.50% major: ~0.04% minor: ~0.46%
There's 7 years of history on their status API. https://status.github.com/api/daily-summary.json
I wouldn't even put it in the 99% (3.7 days) uptime category either.
It is just very public when they go out.
Steam, Blizzard, Activation are down at least 6 hours a week. While Bank of America is offline 24hours/month. Scheduled downtime is still downtime.
Except in the SLA.
I've argued more than once when watching a vendor announce "emergency scheduled maintenance"(!) as an outage is looming.