Google has announced that Stadia players can now stream 1440p (1080p) content if they have the appropriate hardware and internet connection. You need a monitor with a screen resolution of 1440p or 4K or a 4K television with connected Chromecast Ultra to be able to stream with such a high resolution.
In addition to the correct hardware, players must also have an active Stadia Pro subscription and be connected to a network with an average speed of 35 Mbit / s or higher. However, keep in mind that the cellular connection is not neglected and you need a relatively stable Wi-Fi connection that can bear the cost of consuming an average of 20 GB of data per hour when playing 4K games in Stadia.
You also need to ensure that the Windows computer or Chromebook on which you are enjoying Stadia streaming at 1440p resolution can VP9 hardware decode. With Stadia Pro you naturally also get advantages such as 5.1 surround sound and HDR graphics (High Dynamic Range).
Source: Stadia Community