https://www.polygon.com/2017/9/16/16320052/playerunknown-battlegrounds-concurrent-users-steam

One week after surpassing one million concurrent users on Steam, Playerunknown’s Battlegrounds has now set the all-time record for concurrent players.

The game — which, again, is in early access — peaked at 1,348374 concurrent users today, displacing Valve-published Dota 2 for the top figure all time.