Not a factory GTR. GTR's were based on 924's and have turbo 2.0'x not 2.5L 944 engines. That one also has a 944 body. The GTR was a one off body for that car.
There were no factory "944 GTR"s. They were all 924's. There were one or two 944 turbo cars built for IMSA in the late 80's but they did not have normal 944 body work like this one, they had obvious fiberglass bodywork with flares to house 14 inch wide tires.
Pic of a 924GTR:
