It is unclear when the game will be launched on Stadia, but the tweet suggests that it could take place in the next few weeks or months. Apparently this will take place roughly around the same time (or possibly close to) when the version for the PS5 and Xbox Series X is expected to be released.
Given that the Xbox Series X was recently confirmed for November, we imagine that it could be later rather than sooner, but we’ll have to wait since nothing official has been announced yet. That being said, getting GTA 5 on Stadia could be a huge deal for Google as it would tempt gamers to use the company’s services, especially if they did not play the game before or are looking to play it through a different medium.
https://twitter.com/Rockstar_Mag/status/1294576199600156673
However, we should point out that gamers will still need to buy the game because unlike Microsoft’s Xbox Game Pass Ultimate that provides access to unlimited titles for a fixed monthly subscription, Stadia does require gamers to purchase the game in full.