Running between Kadıköy and Sabiha Gökçen Airport, it is the first rapid transit line operating on the Asian side of Istanbul.

The M4 mostly runs under State road D100, parallel to the Istanbul-Ankara railway and is entirely underground.

A plan to build a subway line on the Asian side of İstanbul was approved in 2005.

[4] The M4 opened on 17 August 2012 with a large ceremony in Kadıköy, attended by Prime Minister Recep Tayyip Erdoğan.

The stations Kadıköy, Ayrılıkçeşmesi, Ünalan and Göztepe are situated below sea level.

The Operation Control Center of the line is situated in Esenkent and the depot is located in Maltepe.