https://www.pcgamer.com/mod-brings-cyberdog-rex-from-new-vegas-to-fallout-4/

You probably remember Cyberdog Rex from Fallout: New Vegas. Rex was a former police dog who was cybernetically enhanced, and while many of his parts were replaced with robotics he remained 100% A Very Good Boy. A quest in New Vegas involved finding Rex a replacement brain, as his organic one had begun to deteriorate.

While Fallout fans also love Dogmeat, it's nice to see Rex again, and you can bring him to Fallout 4 with the Project Cyberdog Rex Dogmeat Replacer mod created by Shadowliger. This is a replacer mod and is a visual change only, though the modder is apparently working on a larger Cyberdog mod, which is detailed on the mod's page: