That is not a match, look at the slight arc on the bottom of the piece and how the GS is arrow straight. Also, the bottom of the piece in question is somewhat concave on the bottom and the GS is convex.

To top it off, it is the wrong side of the car.

What is this?

This is most definitely NOT a Lexus GS Exhaust tip. Sure the outside is the same, but the inside seams do not match up and the only side that this would match to on the lexus is the DRIVERS side. Here is an up-close GS: