As described by Tesla:
Our most advanced Autopilot feature ever, Navigate on Autopilot is an active guidance feature that, with driver supervision, guides a car from a highway's on-ramp to off-ramp, including suggesting lane changes, navigating highway interchanges and taking exits. It's designed to make finding and following the most efficient path to your destination even easier on the highway when Autopilot is in use.
The driver is still supervising, and will need to confirm before the car changes lanes, but overall it could mean requiring much less interaction on these closed-access highways. Despite controversy as a result of crashes and occasional complaints, Musk said that until now Autopilot has focused on increasing safety. Even though the "full self-driving" option may be gone from Tesla's website, it's clearly still a goal for the company.
Update: Tesla has published a blog post that explains the feature further, how to use it and includes a video showing how to engage it. Drivers will need to enable the feature in their Autopilot menu, and it has four settings for speed based lane changes (Disabled, Mild, Average, or Mad Max) and will prompt to change lanes either to keep the car on its route, or to stay closer to its target speed.
According to Tesla, "future versions of Navigate on Autopilot will allow customers to waive the confirmation requirement if they choose to," and its future AI chip will enable full self-driving capability on the platform. In another tweet, Musk predicted that waiving the confirmation for a lane change could arrive once "safety looks good" after about 10 million miles of driving with the feature.