This is why Face unlock might come to Pixel 6 Pro and not the Pixel 6
The Pixel 6 Pro uses the Sony IMX 663 imaging sensor vs the Pixel 6’s IMX355. And there is a big difference between the pair as the former supports dual-pixel auto-focus (DPAF) while the latter doesn’t. As 9to5Google notes, ever since the Pixel 2, Google has used dual-pixel auto-focus to create depth maps for Portrait Mode with just one lens.
The hardware used on the Pixel 4 series to create a 3D map of the user’s face
Snag the Google Pixel 6 Pro
“If one imagines splitting the (tiny) lens of the phone’s rear-facing camera into two halves, the view of the world as seen through the left side of the lens and the view through the right side are slightly different. These two viewpoints are less than 1mm apart (roughly the diameter of the lens), but they’re different enough to compute stereo and produce a depth map.” And don’t forget that the Pixel 6 Pro sports multiple cameras on the back
However, unless Google placed a flood illuminator somewhere inside the phone, Face unlock would not work in low-light conditions. But there still is the under-display fingerprint scanner that could be employed when Face unlock can’t be used.
There is no guarantee that Google will add Face unlock to the Pixel 6 Pro
Remember, the iPhone and the Pixel 4 line have only one biometric method for unlocking those devices and thus the flood illuminator is/was a necessity. And just because Google itself says that depth maps are possible using PDAF doesn’t mean that Google will use this methodology to deliver some sort of secure facial recognition to the Pixel 6 Pro.