Android TV 13 is officially launched. However, it is still not available for any consumer devices as of now.
This launch should be considered a developer milestone because the Android TV updates are slower and have a less broad schedule.
Android TV 13 features

The service UI remains the same and it now sports a user-adjustable resolution and refresh rate on supported HMDI devices. It also has improved power saving on an OS level.

Other features include:
- AudioManager API
- Keyboard Layouts API
- Privacy and accessibility improvements
To clarify, it is still not sure when Android TV 13 will become available for consumers, but for now, if you are a developer, you can start using the full-release OS on your ADT-3 dev kit or Android Emulator for TV.
You can also check out the full changelog here.