[6] Up to six pairs can be combined into a 12-car train formation, however due to the relatively short length of the platforms (especially on the new Länsimetro extension), at most only two pairs (giving a 4-car formation per train; and prior to the Länsimetro opening in 2017 three pairs resulting in 6-car formations could also be seen during rush hour) can be combined for passenger service.

Any Helsinki metro train types can be combined mechanically, such as for towing.

The M100 series is the first train in the world to use VVVF propulsion inverters, developed and manufactured by Strömberg.

[4] The first three units (cars 101–106; nicknamed "nokkajuna", "beak trains") were constructed as prototypes in 1977 and had some minor technical differences compared to the later units.

[2] The M100s were refurbished twice: first in 2004–2009, at the Talgo Oy (now Škoda Transtech) rolling stock works at Otanmäki and secondly in 2019-2022 by VR FleetCare at its Ilmala depot,[7][8] to extend their lifetime until their planned retirement in 2030, by which time the class will be almost 50 years old.