On 26 August 2020, the second line was split into two portions: the M2 line, running from Vitosha station to Obelya station and the M4 line, running from Obelya to Sofia Airport. The trains continue to run the length of both lines but on maps and other metro signage the M4 line is gradually being introduced. The split is in preparation to the future construction of the Moderno predgradie station, that is supposed to permanently separate the lines and will allow them to have independent timetables.