Many Android OEMs have adopted in-display or under-display fingerprint scanners in the last few years, including Huawei, OnePlus, Samsung and Xiaomi, to name but a few. Google returned to the capacitive fingerprint scanner with the Pixel 5, having experimented with a 3D face unlock method on the Pixel 4 series. However, the Pixel 4 and the Pixel 4 XL are the only Pixel smartphones to feature anything other than a capacitive fingerprint scanner.
Now, XDA Developers has discovered references to Google adding support for an under-display fingerprint scanner in the second Android 12 developer preview. According to the website, Google has included UdfpsControllerGoogle classes within the SystemUIGoogle app, with Udfps an acronym for an under-display fingerprint scanner. Apparently, these classes belong to com.google.android.systemui, which suggests that Google plans to use an under-display fingerprint scanner in a future smartphone.
Additionally, Google has integrated the Pixel series' fingerprint scanner swipe for notifications gesture within Android 12. As Mishaal Rahman has demonstrated, this gesture works system-wide in the latest Android 12 developer preview, effectively replacing the fingerprint gesture.
These changes do not guarantee that future Pixel smartphones will have an under-display fingerprint scanner. OnLeaks has already shown that Google will persist with a capacitive fingerprint scanner on the Pixel 5a, for example. However, an Android 9.0 Pie beta build foreshadowed Google re-introducing wireless charging to its smartphones as of the Pixel 3 series. Hence, we would not rule out Google releasing the Pixel 6 with an under-display fingerprint scanner.
Android 12 should make it simpler for community developers to enable under-display fingerprint scanners in custom ROMs, too. Ultimately, even if Google opts for a different biometric authentication method with the Pixel 6, the changes within Android 12 are good news for AOSP and custom ROMs.