Is there open-source code available?

A full open-source implementation, named Genie, is currently under development by the MITOGEN group (https://mitogen.github.io/).

The code can be found here: https://github.com/mitogen/genie

The core compression technologies that will be integrated into the Genie code can be found here: https://mitogen.github.io/software/

Note that the Genie project aims at implementing only a subset of the functionalities of the MPEG-G standard and not the entire specifications.