WSJT-X 2.1 RC5, the first one to support JT4 contesting mode has now been released for download.
The home page for the software is here: https://physics.princeton.edu/pulsar/k1jt/wsjtx.html
Direct download for Windows: https://physics.princeton.edu/pulsar/k1jt/wsjtx-2.1.0-rc5-win64.exe