[1] Of the original 22 metro stations, nine are underground, twelve are elevated, and one is at street level.
[3] On 28 March 2020, the first part of the M4 line opened, adding two additional stations and an increased number of trains on the København H - Østerport part of the City Circle Line.
[3] On 22 June 2024, the M4 was extended to Sydhavnen adding five new stations south of København H with a new southern terminus at København S. The system is owned by Metroselskabet, a company owned jointly by the municipalities of Copenhagen and Frederiksberg, and the government of Denmark.
The M4 was originally planned to service Trianglen, Poul Henningsens Plads, Vibenshus Runddel and Nørrebro stations on a temporary basis.
[9] As the built up areas of Nordhavn expand towards the North-East, no less than 9 versions of a future extension have been examined.