The Diablo IV release date was leaked online ahead of The Game Awards 2022, and the file size was also confirmed via the Microsoft Store.
Twitter user Lumia Updates is known for sharing leaks from Microsoft Store or official website. In the past they were pretty accurate. They provided a release date and file size of Diablo IV, which is usually available in the Microsoft Store.
The game will be available on June 5, 2023, the release date could be between June 5 and June 6 due to time zone differences, but for now this is an unofficial confirmation. As Blizzard reveals more details about the game at The Game Awards, a release date is expected to be announced at that time and pre-orders will begin with it.
File size 4 also confirmed: The game is about 80GB in size. This file size is quite large for a game like Diablo 4, but given the amount of content a game typically offers, it seems appropriate. It is also possible that the game has high quality pre-rendered scenes, which is what caused the file size to increase. This could also be due to support for multiple languages.