(Rumors says they want to buy 40 F-35's)
Not a rumor but confirmed they want 40 F-35's as stated by the MoD himself. Negotiations with the US on the S-400 is still ongoing. It seems that the Turks do not back down as they believe they have the upper hand in the following ways: Kaan flies, 6 F-35's have officially been delivered but not received, down payment for these F-35's has been made and the S-400 doesn't operate in a continued fashion.
According to the MoD, the sites where they want the S-400 to operate from are ready with all the infrastructure in place to accommodate the S-400. From what I get is that the S-400 is a system that will only be given marching orders during heightened tensions and can be made ready to operate in 12 hours time.
But with a new US administration about to start, things can possibly go in various directions. Time will tell.