Two pre-series type 1K sets will be delivered by Stadler Pankow in 2015 under a contract which includes an option for 34 production trains for delivery from 2017 onwards.

The new trains are intended to replace the A3L71 fleet, which dates back to 1972-73. Each four-car set will accommodate 330 passengers and seat 80, with full-width gangways and level boarding to aid accessibility.

The vehicles will be unusual in that they will feature a slightly curved bodyshell. This so-called "ballooning" will allow interior space to be optimised within the constraints of the narrow-profile tunnels. This provides a maximum width of 2.4m, 10cm wider than BVG's existing narrow-profile vehicles.