Abellio awarded Bombardier a £900m contract in August 2016 to supply 665 Aventra vehicles formed into 22 10-car and 89 five-car trains. The fleet will be introduced next year on commuter services from London Liverpool Street to Cambridge, Southend, Ipswich, Colchester, and Clacton.
The five-car train will seat 544 passengers, while the 10-car variant will seat 1145.
The trains will be equipped with at-seat power sockets, USB connectors, passenger Wi-Fi, accessible toilets, seat-back tables and underfloor heating. The class 720s will also feature full-width inter-car gangways and information screens to indicate where there are empty seats.
The order is being financed by leasing company Angel Trains.
In addition to the Aventras, Abellio has ordered 58 Stadler Flit multiple units for regional and inter-city services as part of the complete renewal of the Greater Anglia fleet.