Some users are finding that in addition to SD and HD options to buy and rent, they are also seeing 4K rent and buy options for very select movies. On one thread in the Android subreddit, mikegfx said that he was able to find 4K streaming for “This Is The End,” “Zoolander,” “Star Trek,” “Star Trek Beyond,” and “The Fifth Element”. There is no purchase option for the Star Trek franchises, just indications that it is streamable in UHD.
The recently released Chromecast Ultra is able to stream 4K footage, but it’d really help if we could get a little bit more than 4K YouTube from Google’s native ecosystem. We just don’t know how long it’ll take for Play Movies to drag out extra resolution files, but it’s a start that we’re seeing right now.