Several years after Elon Musk said Tesla rejected eye tracking as a method for measuring driver attentiveness because it's "ineffective," owners of new Teslas are receiving vehicles with the feature active. According to notes in the 2021.4.15.11 update, the cabin camera mounted above the rear view mirror will "detect and alert driver inattentiveness while Autopilot is engaged."
This brings Tesla in line with other manufacturers who include cabin cameras to monitor attentiveness while assists are engaged, instead of only relying on steering wheel torque. Some drivers choose to try and trick Tesla's existing systems, causing the reports of cars on the road with no one in the driver's seat. It's not replacing steering wheel torque for monitoring yet, but we'll see if that changes.
Tesla hacker Greentheonly has monitored Tesla's progress in developing the software that watches drivers, and showed what early versions of the system can recognize in some demonstration videos. A few other videos posted to social media in recent weeks show that drivers are starting to receive deliveries of the reworked Model S and Model X with a "yoke" steering wheel and other changes, so there may be more tweaks to find very soon.