https://www.techradar.com/news/oneplus-6t-is-confirmed-to-have-an-in-screen-scanner

We don’t yet know much for sure about the OnePlus 6T, but one very exciting feature has just been confirmed, namely an in-screen fingerprint scanner.

The confirmation from OnePlus came in an email to CNET, which additionally noted that the feature is called Screen Unlock, will be offered in addition to Face Unlock, and will make the OnePlus 6T 0.45mm thicker than the OnePlus 6 (making for a thickness of 8.25mm overall.)