Close to 26.5 million were logged into Steam at the same time in the last few days.
As initially spotted by SteamDB on Twitter, Valve's platform has broken a new record, then just 26.3 million users. Steam Charts shows that at 14:50 GMT on Sunday, February 7th, there were 26,401,443 people using Valve's platform at the same time. Of that figure, 7,360,553 users were actually in-game at the time.
Valve's official count is 26,401,586.
This is yet more growth, following the platform breaking 25.4 million concurrent users at the start of January 2021 and the huge rise in users that Steam saw during 2020. This will be thanks to the COVID-19 coronavirus pandemic. In February 2020, Valve's concurrent user peak was "just" 18.8 million, meaning that it has seen an eight million person increase year-on-year.
Between January 2018 and February 2020, there was no new record set for simultaneous players on Steam, indicating that this has been driven by the COVID-19 coronavirus pandemic.
While the new record set in January of this year was likely driven by the closing of the Steam Winter Sale and the launch of Cyberpunk 2077, there's no indication what caused this most recent spike.