You probably thought it was already on Steam.
GWENT: The Witcher Card Game on Steam

These days, it seems like you cannot go a month without hearing about how GWENT: The Witcher Card Game was made available on this platform or released such and such new content. You probably already assumed that GWENT was available through Steam already, but you would be wrong. In fact, GWENT has only appeared on PC through GOG and their Galaxy launcher. While it's a fine launcher, some people may have been waiting patiently for a Steam release.

Today is that day.

GWENT: The Witcher Card Game is now available for the PC via Steam. This gives PC players an option of where and how they can play this card battling game. As with every other release of the game, the Steam release is free to everyone who can work and operate a computer.

Today's Steam release also features full cross-play and cross-save functionality. This means Steam players can go up against iOS users, or Android users, or those using the GOG release. If you were someone that played on these platforms in the past, all of your pgoression carries over. Strangely enough, they don't specifically mention the Xbox and PlayStation releases here. However, an older FAQ suggests that cross-play is available from PC to either of those platforms.

Additionally, thanks to an update to Thronebreaker: The Witcher Tales on Steam, from today, players can now earn rewards to use in GWENT by making progress in the Thronebreaker campaign. These rewards include premium cards and vanity items, and will unlock automatically once requisite conditions are met. More information on Thronebreaker rewards in GWENT is available here.