We have talked about 4K for a long time. The very latest hot topic is that Google is going to release 4K content on its Google Play. Now, Google has made it official - 4K video is available for rental or purchase on Google Play Store. However, currently there are only 125 movies available in 4K on Google Play, and these 4K movies are only accessible in the US and Canada.
The 4K movie price of these 125 4K movies on Google Play Store is $7.99 for a 4K rental and $29.99 for a 4K movie purchase. It should be noted that not all titles can be rented and bought in 4K. Sometimes it's just one or the other. According to the Google Play officials, more titles would be made in 4K on Google Play in the near future.
You can watch your 4K Google Play content on a Chromecast Ultra or on Sony Bravia 4K TVs with Android TV built-in. Interestingly, Google does not mention the Shield, which has 4K video output. It's not clear if that's an oversight or the Shield is somehow lacking support at present.