Bayern announced on Thursday that the 23-year-old is joining Los Angeles FC from MLS side Los Angeles FC.
For the past two seasons, Sieb had been on loan at FSV Mainz 05. In the campaign just finished, he scored two goals in 22 league games.
After coming through the youth ranks at TSG Hoffenheim, Sieb joined Bayern in 2020 and made his professional debut in the DFB Cup that same year. From 2022 to 2024, he played for SpVgg Greuther Fürth. Bayern then exercised a buy-back option and gave him a contract until 2027 before sending him out on loan to Mainz.