The two type 1K sets will be delivered by 2015, and the contract includes an option for 34 production trains which will be delivered from 2017 onwards if the performance of the prototypes is satisfactory. 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.