Two 4.3 miles (7 km) of electrified train testing tracks will span an area roughly the size of Gibraltar.
More than 1,000 jobs could be created through the other sites, GCRE said.
It was supposed to be operational in 2025, but was delayed until 2030.
The scheme was inherited by Plaid Cymru when it won the Senedd election in May.
GCRE chief executive Simon Jones said there was demand in the rail industry for the services the company would provide, “but we can’t keep using public money forever, so a decision needs to be made.”
Jones added that there had been “detailed discussions” with the energy and data center company, but said he could not name it due to commercial confidentiality.
GCRE wants to complete these negotiations this year so that the contract can be signed.
“And we should be able to know whether the railway will progress or not the moment we sign this contract,” he told BBC Politics Wales.
“If the government decides they want to do this, if we can fulfill the contract with the data center partner, then in five years we could be in a situation where we see trains running through this facility.”