A new release candidate of MPICH, 4.2.0rc1, is now available on our downloads page. This release includes support for the newly ratified MPI-4.1 standard. See CHANGES for more detailed info.
The full set of git commits since 4.1.2 can be found here: https://www.mpich.org/static/downloads/4.2.0rc1/shortlog
At this stage, only critical bugs will be fixed before the 4.2.0 GA release. Please give it a try and report any issues!