Yes, but unlike the GT3 is has the performance to make it a supercar.
The GT3 is a wonderful street legal track day special, but because it has "only" 500 hp, isn't the fastest car - or even 911 variant - that Porsche makes, and is lacking more brutish performance numbers I consider it a high end sportscar.
EDIT: In the end, I - and I alone - am the arbiter of what is a supercar, and what is not. I have a set of criteria that has been revealed here over the years, and it can be vaguely abbreviated thusly: "I know it when I see it."