As u/paszaQuadceps pointed out yesterday, Counter-Strike: Global Offensive had more players on Steam than Dota 2 for the first time this October (https://www.reddit.com/r/GlobalOffensive/comments/dukwis/csgo_has_surpassed_dota2_in_avg_players_in_the/).
The numbers become even more surprising once you factor in PUBG, once a mastodon with over 3 million monthly players on Steam.
For the first time ever, CS:GO was the most played game on Steam this October! For comparison, CS:GO was still 100k players behind PUBG in August.
Counter-Strike: Global Offensive: 747,937
Dota 2: 739,924
PLAYERUNKNOWN’S BATTLEGROUNDS: 637,870
Steamcharts comparison with CS:GO, Dota 2 and PUBG: https://steamcharts.com/cmp/730,570,578080#1y