New mode from the FT8 folks!! Here is a presentation from the developer Dr. Taylor. He begins with some info on FT8 and then moves to the new FT4 mode.
I believe there were some changes made right after this FT4 presentation. The version of FT4 that will be coming out on Monday is synchronous, on a 6-second cycle, and requires a more accurate clock than FT8. One thing that you can do now, before the program release on Monday, is to make sure that your computer clock is as accurate as possible. The Meinberg NTP program is recommended by K1JT for keeping your clock accurate https://www.meinbergglobal.com/english/sw/ntp.htm
You can check the accuracy of your computer clock by going to www.time.is