In conjunction with the upgrade of the existing signalling system from SACEM to Advanced SelTrac CBTC, MTR Corporation originally planned for 78 8-car trains to be ordered.

The rolling stock order was subsequently increased to 93 trainsets at HK$6.05 billion (US$779 million) on grounds that it provided "better value for money".

[11][12] MTR blamed Thales for the incident by making three errors during the installation, which led to data not being properly established at crossover junction near Central station.

As the contractor for the SelTrac system, Alstom-Thales, failed to deliver a proper software fix for the system, MTR announced in March 2022 that all 93 trainsets would be retrofitted with SACEM so they can begin operations and replace the oldest M-trains servicing the Kwun Tong Line, so that they can be retired on time.

[17][18] The new train sets feature an improved lighting system, new dynamic route maps, double-branched handrails, soft materials for hanging straps, colourful flooring and seats (leaning area, not the seats itself), wider doors, and rubber gangways.