The OnePlus 6T will have an in-display fingerprint reader. This was officially confirmed by the company, which went as far as sharing a screenshot of the lockscreen of the upcoming phone. Face unlock is not going away, instead you will get to choose which method suits you best.
Its not just that check out the date on the lockscreen (hint: its in the future). This makes October 17 the likely unveiling date of the 6T (it is indeed a Wednesday).
The OnePlus 6T lockscreen (official image)
Note that the addition of a fingerprint reader behind the display panel will make the 6T thicker. Not much just 0.45mm extra but OnePlus had to re-arrange the internals to make everything fit.
Alleged photos of the retail box already had the rumor mill buzzing about the in-display fingerprint reader and also the teardrop notch. Its no secret that the OnePlus 6T hardware will be based on the Oppo R17 Pro.