Stadler offers a very successful family of electric multiple units under the name FLIRT, what stands for “Flinker, leichter Intercity- und Regional-Triebzug” (agile, light intercity and commuter multiple unit). They are lightweight units, using Jacobs bogies and having a good acceleration. Considerable parts of the equipment were taken over from the GTW and the first generation of the FLIRT also shared the design of its fronts with the GTW. By June 2023, more than 2,500 had been sold all around the world.

The first units were the RABe 523 the SBB had ordered for the Stadtbahn Zug. Like most FLIRT in use in Switzerland, these consist of four cars with both outermost bogies powered. Others consist of six cars with either two or four powered bogies. The Name “Traverso” designates some sets which have been composed of two permanently coupled four-car sets. Due to several improvements on the inside and outside, several generations of these trains are being called FLIRT 1 to 4 and can be distinguished by the design of their fronts.

SBB now operates a total of 223 of the variants RABe 521 to 524, some of which are also equipped for running in the neighboring countries. In 2022, SBB and Thurbo ordered 286 “FLIRT 4 Evo” which are called RABe 531 to 533 and delivered since 2024. Additionally, multiple private companies like the BLS are also using more than 150 sets in total which are designated RABe 526 to 528.