Joe, K1JT, and his team have released new version of wsjt-x.
It now includes fast FT4 mode mainly made for contest use. Period of FT4 is only 6 seconds, so that will affect to sensitivity that will be worse than FT8, but better than RTTY. Roughly saying the difference of sensitivity drop from FT8 is something like step from JT65 to FT8.
Team has selected "mode letter" to be plus "+". That is same as earlier times was reserved for mode T10 (I think it was JTDX's mode).
That is why cqrlog can handle FT4 qsos directly. It is not optimized, and FT4 must be added to user digital modes, but it should work. This all will be fixed on next update.