YouTube Stories and ARCore's Augnmented Faces API or Snapchat-like filters will let you add layers to Stories like animated masks, glasses, 3D hats and more.
In a Google's blogpost they mentioned, "We are excited to share this new technology with creators, users and developers alike, who can use this new technology immediately by downloading the latest ARCore SDK. In the future we plan to broaden this technology to more Google products."
Google believes that augmented reality helps you do more by overlaying digital content on top of the physical world. AR features would be incorporated in Google Maps and Playground(mode in Pixel Camera).
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The developed filters, in association with ARCore, simulates light reflections for realistic rendering of glasses, keeps the lighting natural and models face occlusions to hide virtual object parts.
Talking about the development process the blogpost mentions, "One of the key challenges in making these AR features possible is proper anchoring of the virtual content to the real world; a process that requires a unique set of perceptive technologies able to track the highly dynamic surface geometry across every smile, frown or smirk."