Stiller is a product of Bayern Munich's youth system and he joined Stuttgart in 2023. The 24-year-old has played 82 games for Stuttgart, in which he has scored five goals and registered 17 assists. Stiller's contract reportedly also includes a release clause set at around €40 million (£34m/$46m), but this release clause becomes valid only from 2026. Until then, Stuttgart holds an option to cancel this release clause by paying Stiller a fee of €2m directly, which effectively allows the club to block offers from other teams by nullifying the clause.