As weird as this may sound, Ferrari seems to be pretty far in development for a Challenge version of the SF90. If this will be replacing the FXXK I do not know. I also do not have any other technical details. I'd like to keep my sources protected, but rest assured this was confirmed by more than a handfull of people at Ferrari. They talked quite openly about it as if is nearing completion in it's development cycle actually which I found quite odd. This wasn't revealed to me but someone close whom I trust.