http://www.pcgamer.com/playerunknowns-battlegrounds-tops-dota-2-in-steam-playercount/

It's no secret PlayerUnknown's Battlegrounds is on a tear—the Early Access battle royale shooter has been raking in sales and drawing new players at an incredible rate. It climbed ahead of CS:GO in player count (over 500,000) less than a month ago, and hit 8 million copies sold earlier this week. Now it's claimed a new, perhaps inevitable victory: surpassing Dota 2 in terms of playercount, making it the top game on Steam (as of this writing).

PUBG's seat in the top slot might not last long: Dota 2 often boasts over a million concurrents on any given day, and is only a little below PUBG at the moment, but this is the first time Bluehole's multiplayer shooter has topped it and it certainly won't be the last.