The 2600-series cars were manufactured by the Budd Company, the same company that made the 2200-series. The fourth of five series of Chicago "L" cars known as the High Performance Family, they are quite similar in design to the earlier 2400-series cars. The cars were first delivered to the CTA in 1981, in time for the upcoming O'Hare Airport extension of the Blue Line.
Currently, these cars make up most of the Blue Line fleet and the entire Orange Line fleet, with some cars also assigned to the Brown Line. Car 3458 can be found on the Brown Line. In June 2014, as more 5000-series cars were being delivered, CTA began to transfer the Red Line's 2600-series cars to the Blue Line due to them being newer than the existing 2600-series Blue Line cars, transferring the Blue Line's older 2600-series cars to the Orange Line as an interim replacement for its 2400-series cars until the Red and Purple Lines are fully equipped with the 5000-series cars. Beginning in October 2014, CTA has also started to transfer some of the Red Line's 2600-series cars to the Orange Line to replace the rest of its 2400-series cars until the Red and Purple Lines are fully equipped with the 5000-series cars.
Adapted from https://en.wikipedia.org/wiki/2600-series_(CTA)