Line 8 was the last line created by the concession of 30 March 1898, and the "déclaration d'utilité publique" was approved on 6 April 1903. The project would connect Opéra with Porte d'Auteuil via Grenelle with a shuttle, similar to the network's other lines. In accordance with the plan to operate Line 7 with a junction on the outskirts of Paris, a branch towards the Porte de Sèvres (today Balard) starting from the Grenelle station was planned to be built subsequently. The trains would alternately run on the two branches.