8.25 is in beta. I’ve no info on when it will be released.
Once it is released, it will take a few days for Amazon to publish the new version. Amazon’s update process is slower than Google’s.
You can subscribe to the Android announcement thread to be notified when new versions are available. Scroll to the bottom of the thread and change “Normal” to “Watching.”
You can also subscribe to the Android TV Beta announcements. If desired, you can download and sideload the beta version of the app. Note that if you sideload, the app will not auto-update when new versions are released. To return to auto-updates, delete the side loaded version and re-load the version from the Amazon store.