Google’s popular Chromecast stick supports 1080p resolution. This prototype from Qualcomm can stream 4K. It utilizes the Snapdragon 800 chip and as for right now is in the early development stages. It’s not clear either if this would run a full version of Android or just a subset.
See the article in Trusted Reviews titled First 4K tablets to launch this year, Qualcomm predicts where Tim McDonough, Qualcomm’s Vice President of Marketing, is quoted as saying:
“The first thing you are going to see [with 4K displays] is tablets…”
“I think there is a good likelihood you will start seeing 4K display tablets in 2015.”