Fortnite has over 40 million players, and has achieved 2 million concurrent users

Update, January 15: In just over a month, Fortnite has picked up another 10 million players.

Another month, another 10 million. Fortnite's growth has been incredible since launching its free-to-play battle royale mode.

"We're just absolutely floored," Fortnite's lead systems designer, Eric Williamson, says.

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 Epic also told us that Fortnite's peak concurents also hit a new high of 2 million.

"We're really thrilled by the excitement for Battle Royale," Williamson told us over Skype. "At the same time we see it as a challenge to continue iterating and improving our game. We've been releasing a lot of updates, almost every week really, to improve the core game and add new gameplay affecting stuff. We don't really have any intention of slowing down there."

from
https://www.pcgamesn.com/fortnite/fortnite-battle-royale-player-numbers