Quick answer: GTA VI will stream through Xbox Cloud Gaming on Xbox One and Xbox Series X|S from 1am ET on November 19, using Series S settings. Streaming to PCs, phones, TVs and browsers isn't supported at launch, and Rockstar confirmed 30fps on all consoles.

Grand Theft Auto VI will be playable through Xbox Cloud Gaming on launch day, November 19, starting at 1am ET. Xbox Wire says that covers Xbox One as well as Xbox Series X|S, so older Xbox One owners can stream it without buying a new console. Cloud sessions use the Xbox Series S graphics settings.
The catch for PC players is where you can stream it. The Verge reports that cloud streaming is restricted to Xbox Series X|S and Xbox One consoles, and Notebookcheck says Windows PCs, phones, smart TVs and web browsers are left out at launch, even though Xbox Cloud Gaming normally supports them. That means no cloud option for Windows handhelds either, at least at launch.
Rockstar also confirmed that GTA VI targets 30fps on PS5, PS5 Pro and Xbox Series X|S, according to The Verge. The PS5 Pro's main extras are ray-traced shadows and PSSR support. Rockstar says the game will fully support Remote Play on PlayStation and Xbox.
A few more details from Xbox:
- GTA VI must be bought separately to stream it.
- Starting November 11, players in supported markets can buy cloud playtime without a Game Pass subscription.
- More Rockstar games, including GTA V and Red Dead Redemption 2, are coming to Xbox Cloud Gaming in the coming months.
Xbox CEO Asha Sharma called the cloud deal the first step in a new 10-year partnership with Take-Two, The Verge reports.