Android Developer Preview 4 for the OnePlus 8 phones features an image of the as-yet-unannounced OnePlus 8T. The device can only be seen from the front and is almost the same as the current OnePlus 8.
The image of the OnePlus 8T is, according to Oxygen Updater, the image shown in the About Phone section of Android. The picture has a low resolution and only shows the front, but there are some differences with the current OnePlus 8. The placement of the buttons is slightly different on the new device and the screen appears to be flat. As with the OnePlus 8, the front camera sits in a hole in the top left corner of the screen.
OnePlus has not yet announced anything about the arrival of the OnePlus 8T. The manufacturer has consistently released T versions of its smartphones in the fall in recent years. The OnePlus 7T and 7T Pro appeared in October 2019. Concrete details about the changes of the OnePlus 8T compared to the current device are not yet available.
Update 16:55: The comparison has been adjusted with an image in a higher resolution. The OnePlus 8T appears to have a flat screen, unlike the OnePlus 8 which has rounded screen edges.