What is it? BMW’s long-awaited third-generation electric car won’t just be electric. The company announced that the upcoming i3 will be the first electric car from a mainstream automaker with an optional range-extending engine.

The i3, formerly known as the MegaCity concept vehicle, is an all-carbon-fiber electric city car planned as the successor to the Active-E, a 1 Series-based electric car that becomes available for select leasing this fall.

BMW did not announce what engine would be used as a range extender, but the automaker did say the engine will not be connected with the wheels. Instead, it will only serve as a generator to produce electricity for the electric motor once the batteries are depleted, much like how the Chevrolet Volt works.

The company says the battery in the all-electric version of the i3 will be good for 80 to 100 miles and that the top speed will be limited to 93 mph. As in the Active-E, the i3’s 170-hp electric motor will be mounted on the rear axle, driving the rear wheels. It is reportedly 40-percent smaller than the motor in the Mini-E.

The car will be about 151 inches long, 79 inches wide, and five feet tall, with a 101-inch wheelbase, making it a little shorter and wider than a Nissan Juke.

When will it be available? 2013.