The 4km extension will run from Mixcoac to Obervatorio where it will connect with Line 1 and the 57.7km Mexico City - Toluca interurban passenger line, which is due to open in 2017. The extension will have two intermediate stations at Valentín Campa and Álvaro Obregón.

The initial 24.5km section of Line 12, which opened in October 2012, has 20 stations and runs from Mixcoac to Tláhuac. Line 12 is the second metro line in Mexico City to have conventional steel wheel/steel rail technology rather than rubber tyres.