Western sanctions on Russia gave the project a massive boost, but coordination between the countries involved has been ongoing for more than a decade. Azerbaijan Railways CJSC (ADY) actively participates in the “Trans-Caspian International Transport Route” International Association of Legal Entities (TMTM) since it established in February 2014.
https://www.neglobal.eu/azerbaijan-and-kazakhstan-railways-working-to-upgrade-the-trans-caspian-international-transport-route-middle-corridor/