I received my K4 today, and I can confirm that the Elecraft K3 X4 rig file seems to work well with the K4. I haven’t had a chance to try everything, but so far so good! As a cautionary note, I did have to load new FTDI drivers to get Windows 10 to recognize the K4 (it had no trouble recognizing the K3 earlier in the morning). Tom W4KX