We knew that the Model S and X use AC induction motors, and that Tesla switched to a permanent magnet motor for cost savings on the Model 3. But it seems the Dual Motor variants of the Model 3 will include an AC induction motor in the front, with the partial permanent magnet motor in the rear. Elon also explains that they test the motors and take the highest performers and give them twice the burn in for use as Performance drive units. This is similar to many other manufacturing processes such as Intel. They are known to rebrand processors which have faulty cache or cores by disabling the bits which do not work and to salvage them as lower performing units.