This is an unprecedented day. On August 24, peak concurrency reached a world record 67,335. About a half ago, however, that record was far surpassed, because the maximum reached 68,593 online-- 1258 more. Before the Summer plateau phase, concurrency was growing an average of 500 users a week. Then this major spike.
The mystery is how it grew so fast. First, though, I should ingest some crow.
A few months ago I speculated that the introduction of the graphics-intensive WindLight contributed to Summer's growth plateau; with such rapid growth, that seems way less plausible. Whatever frustrations it was causing Residents with older computers no longer seems to be significant, at least in terms of aggregate numbers.
In any case, why the sudden growth? Today is a holiday in the US, though to my knowledge, none of the other major user regions have the day off. I'm not aware of any major improvements to the server architecture that would improve in-world experience. (In fact, as I write this, there's news that 350 regions temporarily went down, contributing to a concurrency drop of almost 9,000.)