Google started first the self-driving tests but Tesla is comming from behind with speed. And tesla cars are fast, as Elon said in a video they dont build slow cars. While Google did 1.5 milion miles in 6 years, Tesla is using all the fleet to get data and made 47 milion miles in just 6 month, as of april 2016.
The Tesla Autopilot started as a driver assist function with the intent to become a fully autonomous driving system. Tesla says it expects full self-driving by the end of 2017 same period as the first model 3 cars will get out of production.
Autopilot was available from october 9 2014 on the model S as a tech package option that offered assisted driving and parking capabilities. It included a windshiled camera, radar in the lower grill and ultrasonic sensons in the bumpers that could detect road signs, lane markings and cars and obstacles. For one year most of the hardware just gathered data.
One year later the company released a new over the air update version 7.0 with the nickname Autopilot. It could control speed, autosteer, change lanes and selfpark. Some of these functions where already available on others cars but the self steering really made the dream of self-driving look more real, and a lot of youtube videos appeared showing customers driving teslas on the highway hands free.
In the second generation hardware released in october 2016 they upgraded to a powerfull Nvidia Drive PX 2 gpu that they say will eneable fully seld-driving capabilities. It now includes 8 surround cameras, 12 ultrasonic sensons and front facing radar that can see though the car in front.
You can read more on this on tesla’s official page dedicated to Autopilot : https://www.tesla.com/en_GB/autopilot?redirect=no