[6] Spengler was a leading candidate for an F1 driver's seat based on his performances and also it was thought to help drive up interest in North America for Formula 1.

Norbert Haug Mercedes motorsports director commented that if Spengler were to win the DTM championship he would earn a ride in F1.

[7] Spengler had a strong season, coming into the last race at the Hockenheimring three points behind leader and Mercedes driver Gary Paffett.

[8] Spengler became, alongside Beitske Visser, one of the test and reserve drivers for Andretti Autosport ahead of the 2018–19 Formula E season.

He debuted in the 24 Hours of Le Mans in 2020 for ByKolles Racing, won once for BMW Team RLL in the IMSA SportsCar Championship's GTLM class, and was crowned Italian GT Sprint champion in 2023.

[10] In 2025, Spengler joined Alsatian sports car manufacturer Bugatti in the role of "Pilote Officiel", taking over from Pierre-Henri Raphanel.