The OpenIFS model and accompanying software is intended for use on computers external to ECMWF, though member state users with time on ECMWF computers can use ECMWF systems.
OpenIFS is not open-source despite the name. It's use requires an OpenIFS license from ECMWF.
A license is free and once granted, access is provided to the source code and accompanying files and tools. Full installation instructions are provided on this website. Note that other software packages are required to be installed.
More information is provided on the following links: