Yesterday, tvOS introduced 13.4 Beta 1. Although there were not many significant new features, 9to5Mac found that the new Apple TV hardware device code T1125 appeared in the code of tvOS 13.4 Beta 1.
The current code for the Apple TV 4K is J105a, while the Apple TV HD uses J42d. Using the "T" name, it is estimated that it may be the initial internal test version, maybe the "test machine" rather than the completed version.
According to the files in tvOS Beta, the processor of the new device uses the arm64e architecture, which is the same as the current A12 and A13 processors. The current processor of the Apple TV 4K is A10, which means that the next-generation Apple TV is likely to use the faster A12 or even A13 processors. As for when it will appear, I believe it will not be announced until the Apple conference in September this year.