You can buy Autopilot or full Self-Driving capability anytime via your Tesla Account the required Autopilot software will be added to your vehicle.
You can apply by tapping on Controls > Autopilot > Request the Full Self-Driving Beta program from Tesla, and agreeing to the terms and conditions.
Its Full-Self-Driving Beta is a refinement of Teslas driver-assistance function, Autopilot,
which uses sensors and cameras surrounding a car to help drivers in traffic.
All these features are fully autonomous at this time, though Tesla has said on numerous occasions that
cars equipped with the FSD FSD would ultimately be capable of driving themselves without the need for a driver.
Upgrading the Tesla vehicles cameras to the latest model is required to get a Tesla Model S into the Beta tester FSD club once Tesla rolls out a full-scale version.