[1] He then started in 1991 and 1992 as a works driver for the SMS Schmid Motorsport team with the Audi V8 quattro DTM Evo.

[2] After a four-year break, Haupt started for Roock Racing in the GT2 class of the FIA GT Championship and in the American Le Mans Series (ALMS) in 1999.

[2] At the 24 Hours of Daytona he achieved seventh place and the GT2 class victory together with André Ahrlé, Raffaele Sangiuolo and David Warnock in a Porsche 911 GT2 (Type 993).

[1][2] That year he only took part in an endurance race once with a Porsche 911 GT3 R (type 996) for the Cirtek Motorsport team at the 24 Hours of Daytona, which he was unable to finish due to engine failure.

[1][2][4] In 2018, he competed in the Silver Cup class in the Blancpain GT Series together with Abdulaziz Al Faisal and Gabriele Piana, where he finished in second place.

The following year, the Haupt Racing Team entered the DTM and won the drivers' championship with Maximilian Götz.

[8] In 2024, Haupt competed in the FIA Motorsport Games GT Cup, alongside Finn Wiebelhaus, where they won the main race.