Sign in to the Google Play Movies and TV app on a Sony Bravia 2017 or 2018 UHD TV and an offer pops up to receive two free UHD movies from a selection of 20 or so. Buy, select the UHD version, and the price goes to zero when checking out (make sure it does before you complete; you buy two separately).
This seems to not be advertised here in Australia; indeed it says it's US only but it worked for me. I wasn't even aware of it until I found it messing around with my TV (an X9000E, so it seems more models are included than the terms state).
Saw this the other day, but I could only get one free. Got Blade Runner 2049!