The newer ones (purchased after Feb 2016) support HDMI 2.0 and 4k @ 60Hz, but you’ve got to first enable a special setting. I was able to do this successfully, and since I’m using the DP port on the monitor to connect a different machine, I’m thankful to be able to leverage both ports at 60Hz without having to swap the cable out or use a …

https://www.amazon.com/uni-Thunderbolt-Compatible-MacBook-Surface/dp/B075V5JK36