Apple has already said the company won't send faceprint data to the cloud, which means your face data stays on your phone. (theverge.com)
Faceprints serve as distinct digital identifiers, similar to a fingerprint, that are based on the unique contours of a person's face. (fortune.com)
When the iPhone X was announced, Senator Al Franken asked Apple in a letter «How will Apple respond to law enforcement requests to access Apple's faceprint data or the Face ID system itself?» (thenextweb.com)