Red Dead Redemption 2 was recently released on PC via the Rockstar Games Launcher, Epic Games Store, GreenmanGaming and other retailers, and it launched on a new service today as well - alongside the service itself! As of today, Red Dead Redemption 2 is available on Google Stadia.

Stadia is Google's latest attempt to swim into mainstream gaming by providing players with a new option when they choose how to consume their content. Stadia is a cloud-based streaming service which lets games be played on machines which would lack the hardware required to run the software locally.
The service launched with a library of 22 games upon release, with plans to further expand that in the days, weeks and months to come. Red Dead Redemption 2 is among those launch titles, bringing the highly successful AAA blockbuster's popularity to bare.
While Red Dead Redemption 2 on PC has rather tame system requirements for such a massive, graphically jaw-dropping open-world AAA flagship title, it also requires 150 GB of space on your hard drive, and isn't exactly something you'd play on an unplugged laptop while traveling.
Stadia will allow you to take Arthur Morgan with you on your own adventures. The whole idea behind Stadia is to play anywhere, on anything (that supports Stadia, of course). With the Google Stadia Controller plugged in, you can even stream major AAA hits onto a mobile device and enjoy the game at 60 FPS, 4K with HDR enabled - something that would melt the device otherwise.
Rockstar is offering a number of bonuses for players who purchase Red Dead Redemption 2 on Stadia before the year is over. If you buy it before the 16th of December, you get a bonus of 25 Gold Bars in Red Dead Online, while all players who buy it before the 31st of December get the Outlaw Survival Kit, War Horse, Treasure Map, and more to be used in Story Mode.
Red Dead Redemption 2 will be launching on Steam in December as well.