The construction of Mladost 3 and Inter Expo Center - Tsarigradsko chaussée stations began on 15 February 2009 and was completed on 25 April 2012. The further extension to Sofia Airport comprising two underground and two overground stations and a length of began in 2013, and was completed on 2 April 2015 at the cost of BGN 136,757,630 (EUR 69,923,066), VAT exclusive. This extension was briefly operated as a branch of M1 line, but was soon transferred to M2 line, moving that line's terminus from Obelya to Sofia Airport.