Fizzer knows very well, just never wanted to disclose it.
@DanWL, I don´t have exact definition. Somewhat points in 30-days could be good indicator, but for average 4-5 days a week player those 1000 points from random single real-time game withing 30-days surely ain´t enough.
I would broaden the term "active" in a way it would include either real-time or multi-day games, hopefully some wins (therefore also points) or at least few (for example 2 or 3) participation´s in multi-day games.
A year back or so, I checked randomly players from different Global QM rankings - for example of intervals 999-900, 899-800.. and it did not looked good from active perspective. Hence my guess from QM, considering most active players ought to end up there. Well, yeah some play single-player only, but who does that help to fix a match in QM, increase Ladder players or bring more players to Open-games diplo nonsense, so I would not regard them as active. Having < 100 open games has been pretty solid number in years. Even for years prior to QM.
1v1 Ladder playerbase has been also quite stable. Seasonal has its new wave of lows, even less than 200, compared to ~300 for few years prior to this. My 20 000 is just a guess.