The WRF version 4.0 has been released on June 8th, 2018. All updates are given on WRF model page details of UCAR website.
New version of WRF available: 4.0
Version 4.0 generalizes the new hybrid sigma-pressure vertical coordinate introduced in version 3.9 and set the moist potential temperature as default. New options for physics, PBL, soil especially Noah-LSM, dynamics and memory requirement improvements have been made. WRF version 4.0 can use wrfinput and wrfbdy files from version 3.6 to 3.9.
Check our page (in french) about WRF.