# 17.1. Main updates (not on release branches yet)

This file generally contains all the updates for Open MPI that have not yet appeared on a release branch. It reflects active development, and is therefore a “loose” listing of features and changes. It is not considered definitive.

## 17.1.1. Open MPI version main

MPIR API has been removed

As was announced in summer 2017, Open MPI has removed support of MPIR-based tools beginning with the release of Open MPI v5.0.0.

The new PRRTE based runtime environment supports PMIx-tools API instead of the legacy MPIR API for debugging parallel jobs.

see https://github.com/openpmix/mpir-to-pmix-guide for more information

zlib is suggested for better user experience

PMIx will optionally use zlib to compress large data streams. This may result in shorter-than-normal startup times and smaller memory footprints. It is recommended to install zlib and zlib-devel for a better user experience.