Yep! I play on the FA and Team Muppet servers, and at peak times during the day the server will be almost full (60 players).
But, that's kinda it, I doubt there are ever more than 1k people online at a time. But those same people have millions of XP (I actually have a PR open on the client ATM to abbreviate the XP in the scoreboard, which I think we finally need after 20 years lol)
If you play, make sure you use the etlegacy client, it is backwards compatible with many fixes/improvements.