AppleInsider:

Though it went unannounced at Apple’s WWDC 2018 keynote on Monday, the first iOS 12 beta allows two different people to register their face with Face ID on iPhone X, addressing in part one of the biggest downsides of Apple’s new biometric authentication technology.

While still not as capable as Touch ID in this regard, this is still a welcome way for me to allow my wife to access my iPhone X easily.