If the FX4 thru axle is the same as my FX1, it is a normal quick release but with closed dropouts so that you have to screw the end off and pull the QR out before the wheel will come off. If that is the case, front racks that hang on a longer QR will work once you remove Trek's fixed in position QR nut and replace it with a normal one. I did this right away anyway, since it is faster to get the wheel off.