In his teardown of Gboard v 7.4, Cody saw signs of a new personalized "minis" sticker pack coming. The feature is now live in v7.5.6 beta, which started rolling out today. The new minis stickers are a re-implementation of the selfie stickers that launched on Allo last year — as a matter of fact, many of the options are the same — but instead of one pack, you get two: "Bold mini" and "Sweet mini."
You'll see the "minis" option when you switch to the sticker section of Gboard. A new pack with an exclamation mark will appear at the rightmost of your favorites. Tapping it explains that these minis are customized based on you and offers to create them. You'll have to take a selfie by fitting your face in a square, then some Machine Learning magic kicks in and makes two versions based on your image.
You can customize your Bold mini and Sweet mini by changing the face, hair, eyes, nose, mouth, and more. By default, the minis are added to your favorite sticker packs and show up at the top, but you can re-order them, remove them from favorites, or even delete and re-create a new pack with a different selfie.
The feature is showing up on version 7.5.6 of Gboard, which is still a beta release. You can grab it from the Play Store after you join the beta program, or by downloading it directly from APK Mirror.