Around 340 thousand passengers are expected to be served daily by Metro Line 4, which, when completed around 2029, will radically change the traffic situation in the capital.

Two TBM tunnel boring machines are currently working: one from the Katehaki shaft in the direction of the centre to Evangelismos Station, and one from the Veikou shaft, also in the direction of Evangelismos Station. Each TBM, or Metropontika, digs on a daily basis an average of 15 meters, placing 10–12 "rings," as the permanent concrete lining of the tunnel is called.

This is the largest public project being implemented in the country, with a budget of 1.5 billion euros and consisting of fifteen new underground stations: Veikos, Galati, Elikonos, Kypseli, Dikastiria, Alexandras, Exarchia, Akademia, Kolonaki, Evaggelismos, Kaisariani, Panepistemiopolis, Ilisia, Zografou, and Goudi, with a tunnel length of approximately 13 km and a contractual completion time of eight years from the signing of the contract.

It includes a new Operation Control Centre (OCC), with the prospect of integrating the operation control of the existing Lines 1, 2, 3, and 4 and future automatic new trains and the tram, as well as a new building for maintenance and repairs of the new trains, to be located in available space at the Sepolion depot.

It is planned to supply 20 trains of the Alstom Metropolis series. Following the example of Thessaloniki, the trains will be the first in the Athens system to operate ultra-automatically, without a driver, and with control of their movement by the control centre.

The specifications for Line 4 follow new standards and incorporate new technologies, as many requirements and procedures have changed based on experience from previous projects and the Thessaloniki project.

In total, it is estimated that the operation of New Line 4 of the Athens Metro is expected to move around 340,000 passengers per day, while car travel is expected to be reduced by around 53,000 per day, carbon dioxide emissions are estimated to be reduced by 318 metric tons per day, and 1,216 megawatt-hours of energy will be saved.