On June 9th, 2021 the Message Passing Interface Forum (the MPI Forum) ratified and published the latest version of the MPI Standard. This version "MPI 4.0" adds significant new features to MPI 3.1 from June 2015. The goal of the MPI Forum, simply stated, is to define and advance a widely used standard API for writing message passing programs. This interface, MPI, provides a practical, portable, efficient and flexible way for message passing, which has become the de-facto standard for large-scale parallel programming. The most substantial changes in MPI 4.0 are the addition of large-count versions of many routines to address the limitations of using an int or INTEGER for count parameters, persistent collectives, partitioned communications, an alternative way to initialize MPIusing the new concept MPI Sessions, support for hardware topologies, a new event based tools interface as well as improvements to the definitions of error handling. In addition, there are a number of smaller improvements and corrections.
Find the standard document here
The MPI Forum, with participation from over 40 organizations, has been meeting since January 1993 to discuss and define a library interface standards for message passing. Prof. Martin Schulz, Chair of Computer Architecture and Parallel Systems, has been Chairman of the MPI Forum since 2012.