'FastRail') or M34 is a 74.5 km long planned line of the Istanbul Metro to be constructed in the east-west direction of Istanbul, and is currently undergoing feasibility tests by the Istanbul Metropolitan Municipality.

[2] The line was proposed by Ekrem İmamoğlu, the Mayor of the Istanbul Metropolitan Municipality, in September 2020. it was initially planned to span 62.8 km with 10 stations, operating at a speed of 160 km/h (which was later reduced to 140km/h after the revision), and was initially proposed to run between Halkalı on the European side and Sabiha Gökçen Airport on the Anatolian side.

However, during the Raylı Sistemlerde Büyük Hamle (lit.

'Major Leap in Rail Systems') press conference held by Ekrem İmamoğlu on February 7 2021, it was announced that due to high demand from the Esenyurt and Beylikdüzü districts, the new terminus would be Beylikdüzü, extending to 13 stations, and increasing the length of the line to 74.5km.

[3] On November 9 2022, the Istanbul Metropolitan Municipality revealed the updated route of the line, including detailed designs, revisions, and technical specifications for many of the stations.