Most hybrid vehicles use a continuously variable transmission (CVT) which fully integrates the electric motors and generators. Instead of a CVT, the Sonata uses a 6-speed automatic transmission, and an electric motor takes place of the torque convertor. Powering that electric motor is a U.S. first, lithium polymer battery pack. This saves weight over traditional nickel metal hydride battery packs, increasing efficiency and performance.
Speaking of performance, the reported total power output is a class-leading 209 horsepower, and Hyundai claims the Sonata Hybrid can drive up to 62 mph on batteries alone. Price hasn't been announced, but given Hyundai's track record of coming in below the rest, the Sonata Hybrid should be very competitive.