On Aug 15 2019, Joseph Schuchart via mpi-forum wrote:

On 8/13/19 5:54 AM, Jed Brown via mpi-forum wrote:

...

Few packages will accept a hard dependency on MPI-4 for at least 10 years. MS-MPI still doesn't fully support MPI-2.1, for example, and PETSc only recently began requiring MPI-2.0.

That is a sad truth: I just had a colleague asking me about a >6y old Open MPI release...

It's not just MPI! But it's not as sad as all that. Interfaces that handle upwards compatibility well, like Fortran and MPI, continue to accept old code. And, if people don't have problems with their MPI, there is simply no need for most of them to upgrade - especially if they are not changing that part of their code. Please continue to preserve this tradition! Regards, Nick Maclaren.