As a successor to the class 4 and 5 express locomotives, Karl Gölsdorf developed the class 6, which was his first express locomotive. Like its predecessors, it also had two coupled and running axles each. In order to achieve the required increase in output, Gölsdorf took a different approach to arranging the boiler, which was inspired by the famous number 999 of the Pennsylvania Railroad, among others.

Instead of arranging the boiler very low, as was previously the case, to achieve the smoothest possible running, a boiler with a larger diameter was used here, with the firebox standing completely above the frame. Thus, a continuous output of up to 900 hp could be achieved through a larger grate and evaporation surface. In addition, a two-cylinder compound engine with the high-pressure cylinder on the right side was used.

A total of 68 examples were built between 1894 and 1898, which reached speeds of up to 130 km/h in test drives. Nevertheless, the certification was only granted for a speed of 90 km/h, which was sufficient in Austria. The BBÖ still had 20 units in service after the First World War and used them until 1932. 28 units were in service with the CSD until 1938 as series 264.0 and nine more with the PKP as Pd12.