While UHD streaming is coming to Microsoft’s operating system, it comes with some conditions. These include using Microsoft’s Edge browser and your system needs to be running 7th-generation Intel Core processors (Kaby Lake). The former is an easy enough to get your hands on, the latter requires a bit of a search since there aren’t that many laptops yet that have 4K displays and the new Intel processors.
You can see the 4K support as a means to market Microsoft’s latest products but also because of DRM requirements imposed to avoid streams being captured and redistributed illegally. The newest hardware decryption features don’t work on older Intel processors but Kaby Lake supports 10-bit HVEC, which is a popular 4K video codec. Either you’ll have to upgrade your PC to watch Gilmore Girls in 4K or get a Chromecast Ultra or Roku device to stream 4K with Netflix.