According to SteamDB, on January 7 there were over 14,207,039 gamers running Valve's Steam service at the same time. This is the highest number of concurrent players on Steam ever, and it shows that more and more users are adopting PC as a gaming platform.

Steam has just hit a new record of (over) 14 million concurrent users. https://t.co/D6WDHbz0B4

— Steam Database (@SteamDB) January 7, 2017

As far as milestones go, Steam hit 5 million concurrent users in 2012, 8 million in 2014,  then 12 million in 2015. Even though not all these users were necessarily in a game, just running Steam, it does give a figure of just how much Steam's install base in growing.

During the 14 million user peak this week, Dota 2 had the highest player count with 951,942 users playing. Counter-Strike: Global Offensive was in second place with 675,195 players, and Grand Theft Auto V had 116,230 people logged in.

Since January 7 the concurrent user numbers have dropped back into the 13 millions. However, when the Steam Summer Sale rolls around, we're sure to see that number rise again.