Audi has secretly bought the remaining 75% of the shares in the Sauber F1 team but is not yet convinced that Valtteri Bottas or Zhou Guanyu should get a contract for 2025. Question marks are lingering over the driver line-up in Hinwil, Switzerland for next year with Bottas and Zhou both out of contract. Sauber signed Bottas to a three-year deal to join while operating as Alfa Romeo in 2022. While Zhou agreed to a new one-year deal last September. Now, the Finnish and Chinese racers are fighting for their future at Sauber, now operating as Stake F1 Team, ahead of Audi taking over the outfit in …