Steam's concurrent players count hit 30 million for the first time on October 23, 2022.
Record Screenshot
The final number stopped at 30,032,005.
March 2020 Record
Steam officially launched in September 2003, 12 years later in June 2015 the number of concurrent players reached 10 million for the first time, and after another 5 years in March 2020 exceeded 20 million, then from 20 million to 30 million in only 2 and a half years (the number was once approaching 30 million early April this year, just short of 10,000 more)
Source: SteamDB