As Wilhelm Schmidt's superheater went into series production, Karl Gölsdorf modified the Class 329 into the superheated variant 429.

In spite of the small superheater area, problems arose with the slide valve on the low-pressure side.

At the same time a two-cylinder simple variant with piston valves was tried, of which in the end 197 units were procured by the kkStB (429.900–429.999 and 429.1900–429.1996).

The Austrian Southern Railway Company (Südbahn) procured six compound locomotives (with piston valves), that were numbered 429.01–429.06.

The ČSD in Czechoslovakia converted all its compound locomotives (27 of the first series, 57 of the second) into two-cylinder engines.