The class 4 was the first express locomotive directly ordered by the kkStB. They had the wheel arrangement 4-4-0 and a driver diameter of 1,820 mm. Based on the class 1 that had been built since 1877 for several railway companies, it had the same cylinder dimensions, but the drivers had been enlarged by 100 mm. A total of 180 were built directly for the kkStB between 1885 and 1896 by four manufacturers. 13 were rebuilt from the class 3 that had originally been ordered by the KFJB and 20 came from smaller railways. Five fairly similar locomotives were used by the EWA as IIa.

After World War I around 50 came to Czechoslovakia and formed ČSD class 254.2. Around 30 now were in Poland and became PKP Od13. Twelve came to Italy and formed FS class 543. The kingdom of the Serbs, Croats and Slovenes received 18 and finally, a few came to the Romanian CFR. The locomotives which stayed in Austria were still designated class 4. The BBÖ retired the last one in 1930 and the ČSD did the same in 1937.