The trains have the ability to operate on the third rail-powered sections of the network, with some units carrying onboard batteries to allow use on unpowered track.

[15] In January 2016, Merseytravel announced that a total of five rolling-stock manufacturers had been shortlisted to build the new fleet – Bombardier, Siemens, CAF, Stadler Rail, and a consortium of Mitsui, Alstom, and the East Japan Railway Company.

The purchase was financed by Liverpool City Region itself, rather than an external agency such as a bank or rolling stock leasing company.

[11] These adaptations were performed under a rolling programme between October 2018 and May 2019; changes included adjustments to 97 platforms at 56 stations across the Merseyrail network, along with track realignments and other refinements, primarily for the purpose of improving passenger accessibility.

New bulk power supplies were installed, along with eight new substations and miscellaneous cable upgrades, to provide greater quantities of electricity.

[21] Accordingly, while the fleet was initially to be launched under driver-only operations, in September 2018 it was announced that there would be a second member of staff on board, ending a two-year dispute between the National Union of Rail, Maritime and Transport Workers (RMT) and Merseyrail.

The Liverpool City Region Combined Authority announced that the battery-powered trains will run to the new Headbolt Lane station at Kirkby, which opened on 4 October 2023.

[11] They have a higher rate of acceleration, yet use 20% less energy than the old rolling stock, due to increased system efficiency and a reduced weight, being roughly 5.5 tonnes lighter.

The introduction of the Class 777 is reportedly set to achieve a 10% reduction in journey time over older stock, attributed to its greater rate of acceleration.

[11] There is also an emphasis on shared data; each train will actively monitor the number of passengers on board and relay this to Merseyrail's Sandhills control centre, allowing for more informed and responsive management of the network.

For accessibility purposes, all doorways have been outfitted with sliding steps that move into position when the train is stopped at a platform, enabling passengers using wheelchairs to board and disembark without relying upon a separately deployed ramp.

[11] The passenger facilities are much improved over legacy stock, each carriage being fitted with modern amenities such as electrical and USB sockets, as well as bike racks.

[11] As part of the bespoke design, an LED letter 'M' has been sandwiched between the headlight clusters, illuminating yellow on the front of the train, and red on the rear.

This is in addition to the backup battery set that will be fitted to all Class 777 units from new, as these will only have capacity for short-distance low-speed movements around depots and maintenance facilities.