On January 2 Steam hit 25.4 million concurrent users (opens in new tab), a record that lasted just over a month. As of today, the record now stands at 26,401,443 (opens in new tab). That's connected users, not players in-game, however. There were 7.3 million people in-game at the time, which is under the record 8.1 million in-game players at the end of March 2020, back when the COVID-19 pandemic was first going global.
The top five games by playercount at the time were Counter-Strike: Global Offensive, Dota 2, PlayerUnknown's Battlegrounds, Apex Legends, and Tale of Immortal, a Chinese RPG that's currently only available in Simplified Chinese (opens in new tab). This weekend marked the beginning of lunar new year vacations for some people, which likely helped this latest boost, although Steam's numbers have been rising steadily for almost a year now.
Steam's concurrent record was only 18.8 million in February 2020, and it took two years to get there from the previous record of 18.5 million when PUBG was taking off. The current rate of growth is a significant change.
As Valve said in its 2020 year in review (opens in new tab), in which it celebrated having 120 million monthly users, "While Steam was already seeing significant growth in 2020 before COVID-19 lockdowns, video game playtime surged when people started staying home, dramatically increasing the number of customers buying and playing games, and hopefully bringing some joy to counter-balance some of the craziness that was 2020".