AFAICT from Google satellite view, all tracks on the
Fremont Tesla factory property have been removed, and there are no loading facilities (though many empty tracks) in the adjacent Warm Springs yard. Some years ago, I did hear that Tesla got into a spat with UP, and started trucking everything; if rail was going to be used for part of the trip, they would truck it to Richmond for loading onto BNSF.
Tesla Giga Texas also appears to have no rail service, even nearby. Though that might be the battery factory. Even then, Giga Nevada (batteries) is in an industrial park with rail service, but it is conspicuously absent at Tesla.