https://wccftech.com/download-tvos-13-gm/

Believe it or not but you can download tvOS 13 GM for Apple TV HD and Apple TV 4K right now.

While we are still a few days away from the real-deal final release, developers can get in on the action early by taking the tvOS 13 GM for a spin. This is highly likely the same build that will be shipped to end users later on in the month. If there are going to be slight changes here on in, we will most probably see them in the final release of the software.