Version 4.0.2 can be downloaded from the main Open MPI web site:
https://www.open-mpi.org/software/ompi/v4.0/

Major Changes include:

• Update embedded PMIx to 3.1.4
• Enhance Open MPI to detect when processes are running in
  different name spaces on the same node, in which case the
  vader CMA single copy mechanism is disabled. Thanks
  to Adrian Reber for reporting and providing a fix.
• Fix an issue with ORTE job tree launch mechanism. Thanks
  to @lanyangyang for reporting.
• Fix an issue with env processing when running as root.
  Thanks to Simon Byrne for reporting and providing a fix.
• Fix Fortran MPI_FILE_GET_POSITION return code bug.
  Thanks to Wei-Keng Liao for reporting.
• Fix user defined datatypes/ops leak in nonblocking base collective
  component. Thanks to Andrey Maslennikov for verifying fix.
• Fixed shared memory not working with spawned processes.
  Thanks to @rodarima for reporting.
• Fix data corruption of overlapping datatypes on sends.
  Thanks to DKRZ for reporting.
• Fix segfault in oob_tcp component on close with active listeners.
  Thanks to Orivej Desh for reporting and providing a fix.
• Fix divide by zero segfault in ompio.
  Thanks to @haraldkl for reporting and providing a fix.
• Fix finalize of flux compnents.
  Thanks to Stephen Herbein and Jim Garlick for providing a fix.
• Fix osc_rdma_acc_single_intrinsic regression.
  Thanks to Joseph Schuchart for reporting and providing a fix.
• Fix hostnames with large integers.
  Thanks to @perrynzhou for reporting and providing a fix.
• Fix Deadlock in MPI_Fetch_and_op when using UCX
  Thanks to Joseph Schuchart for reporting.
• Fix the SLURM plm for mpirun-based launching.
  Thanks to Jordon Hayes for reporting and providing a fix.
• Prevent grep failure in rpmbuild from aborting.
  Thanks to Daniel Letai for reporting.
• Fix btl/vader finalize sequence.
  Thanks to Daniel Vollmer for reporting.
• Fix pml/ob1 local handle sent during PUT control message.
  Thanks to @EmmanuelBRELLE for reporting and providing a fix.
• Fix Memory leak with persistent MPI sends and the ob1 "get" protocol.
  Thanks to @s-kuberski for reporting.
• v4.0.x: mpi: mark MPI_COMBINER_{HVECTOR,HINDEXED,STRUCT}_INTEGER
  removed unless configured with --enable-mpi1-compatibility
• Fix make-authors.pl when run in a git submodule.
  Thanks to Michael Heinz for reporting and providing a fix.
• Fix deadlock with mpi_assert_allow_overtaking in MPI_Issend.
  Thanks to Joseph Schuchart and George Bosilca for reporting.
• Add compilation flag to allow unwinding through files that are
  present in the stack when attaching with MPIR.
  Thanks to James A Clark for reporting and providing a fix.

Known issues:

• There is a known issue with the OFI libfabric and PSM2 MTLs when trying to send
  very long (> 4 GBytes) messages. In this release, these MTLs will catch
  this case and abort the transfer. A future release will provide a
  better solution to this issue.