Incorrect. Out of the three Sierra hosted at LLNL that have the "4 GPUs per node" you're talking about, two of them are in fact accessible from the public Internet. One is in Collaboration Zone CZ (Sierra/lassen), another is in Restricted Zone RZ (Sierra/rzansel). Only one of the three is classified (Sierra/shark), and even then it's still sshable when one's logged into SecureNet.