A total of 200 kilometres (120 mi) of new tracks and 68 new stations are to be added, serving a projected 2 million passengers a day.

[7] The first public inquiry, focused on the southern section of Line 15 from Pont de Sèvres to Noisy–Champs, was held from October to mid-November 2013.

To ensure better commuter service to the inner northeastern suburbs, a six-station, 5.4-kilometre (3.4 mi) eastern extension of Line 11, not considered part of the Grand Paris Express project, opened from Mairie des Lilas to Rosny-sous-Bois.

[11] It provides connections with the RER E and an eventual extension of Île-de-France tramway Line 1, which better links central Paris with the commuter hub of Châtelet–Les Halles.

[12] Automatic train operation was not implemented with the Rosny extension, although the RATP and STIF had considered the possibility of adding it later on.

Île-de-France Mobilités planned to replace the aging fleet of Line 11 with MP 14 series trains around the time of the opening of the extension to Rosny-sous-Bois.

The extension travels southeastward from Olympiades to Maison Blanche, interchanging with Line 7's Villejuif branch, and opened on 24 June 2024 (again, just a month before the 2024 Summer Olympics).

[20] With both extensions complete, it is expected that Line 14 will eventually be merged into the proposed Grand Paris Express system.

This new stock is in eight-car train formations, longer than previously employed anywhere on the Paris Métro but which the length of all Line 14 stations was planned for.

It was later included in the red line project of the Grand Paris public transportation network, introduced by French President Nicolas Sarkozy in 2009.

[26] It will create a loop connecting Noisy–Champs to Champigny, passing through Champigny-sur-Marne, Créteil, Villejuif, La Défense, Saint-Denis and Rosny-sous-Bois.

On 22 February 2018, a new timeline is announced by Prime minister Édouard Philippe:[27] In 2013, the government led by Ayrault proposed this timeline for the line 15 project:[28][29] The proposed rolling stock for line 15 is a new automated design, using conventional steel wheel on steel rail technology and overhead electrification, with a width of 2.80 metres (9 ft 2 in).