FT4 is an experimental digital mode designed specifically for radio contesting. Like FT8, it uses fixed-length transmissions, structured messages with formats optimized for minimal QSOs, and strong forward error correction. T/R sequences are 6 seconds long, so FT4 is 2.5 × faster than FT8 and about the same speed as RTTY for radio contesting.
Further information on FT4 is at
http://physics.princeton.edu/pulsar/k1jt/FT4_Protocol.pdf
http://www.southgatearc.org/news/2019/april/new-digital-mode-ft4.htm