The Mi 8 is rumoured to have a feature i.e. a notch on top of its display that could house 3D depth-sensing modules for face recognition, which is similar to iPhone X, which may not be in Mi Mix 2S.
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However, if one closely observes the buildings in the background of the teaser image, they will notice that one of them is actually a thin-bezel smartphone with rounded edges.
There also seems to be a power button on the right edge of the device.
We are not sure about this feature for Mi Mix 2S.
ALSO READ:- MI 8 EXPECTED SPECIFICATIONS
Slashleaks also leaked a video that Mi 8 may come with an in-display fingerprint sensor.
Mi 8 in-display fingerprint video:- http://bit.ly/2IRrZQW