Stadia Base is the free version of Stadia and it is launching in 2020. With this version of Stadia you get as the name suggest the Base version of Stadia. You get 1080p but still at 60fps and stereo sound. Multiplayer is included in the base version of Stadia. Access to free to play games is not included.
The best way to compare Stadia Base and Sadia Pro is like comparing the PS4 to the PS4 Pro. You are paying for better resolution and Playstation Plus like features like “free” games each month and discounts on some games.
We would recommend if you are on the fence about Stadia and the Pro service to wait and try Stadia Base next year. For more information on Stadia Pro click here.
Following the AMA on 18th July this page was edited to change access to F2P is not included.