Thanks for reaching out to the Chromecast Community forum!
When you say 4k Google Chromecast, are you pertaining to the Chromecast with Google TV? If yes, you can go to the Apps option and search to see if the Spectrum app is available. However, upon searching on the Spectrum website, it looks like that Spectrum TV app is only available to download from a phone or tablet then you can cast it to your TV using Chromecast. Check the information here. Also, I suggest you contact Spectrum for additional help.