I have seen examples of other particles that decay into gluons but do gluons themselves ever decay. Since gluons are not composed of anything else I assume they are fundamental.
On there other hand some fundamental particles decay and some do not i.e the photon. But on the other other hand some non fundamental particles do not decay either. i.e proton.
Maybe I am getting tangled up in semantics. Instead of decay would transformation be a better description.