Tesla described HW2 in October, writing:
Eight surround cameras provide 360-degree visibility around the car at up to 250 meters of range. Twelve updated ultrasonic sensors complement this vision, allowing for detection of both hard and soft objects at nearly twice the distance of the prior system. A forward-facing radar with enhanced processing provides additional data about the world on a redundant wavelength, capable of seeing through heavy rain, fog, dust and even the car ahead.
When the $35,000 Model 3 [hopefully] enters production later this year, it too will have all the necessary hardware for Level 5 autonomous operation.
But before you start jumping for joy at the prospect of sitting behind the wheel and letting your Model S complete an entire trip on its own, we have to temper your expectations. This update merely brings Autopilot for HW2 vehicles up to parity with the system available to older vehicles. The software update enables Traffic Aware Cruise Control, Forward Collusion Warning and Low-Speed Autosteer (currently in beta).
Tesla writes in the release notes for the update:
These features operate on a new hardware and software platform. Therefore, their rollout will be measured and cautious until we have generated confidence across several hundred million miles of real-world usage. Enhanced Autopilot will become better over time as this experience is gained and corner cases are addressed. In the meantime, it is particularly important that you remain vigilant and in control when using driver assistance features.
Once Tesla unlocks all functionality for Autopilot, HW2 owners will able to sit back, relax, and take trips like this to and from work every day, or perhaps to visit your family on the other side of the state: