There is hardly any difference from what I've heard, other than the name, exterior and age. The only other differences are that the GT is lighter than the Glanza, but the heavier Glanza has an extra blade on the turbo to make up for it in torque. Heard some people say that the suspension is slightly updated on the Glanza, what with it being newer, but I'm uncertain about that. It's a matter of personal preference really. They're the exact same performance stats, it's just a matter of what you like the look of the most. The only other thing is that the Glanza seems to have more aftermarket exterior bits, but thats it really.