Gates currently offers Poly Chain GT Carbon belts that are designed to run in Poly Chain GT2 sprockets. There are also PowerGrip GT3 belts designed for PowerGrip GT2 sprockets. What's with the GT, GT2, and GT3?
It's easy to get caught up in the product line names, but don't let it throw you off. "GT" stands for "Gates Tooth" which describes the belt's patented curvilinear tooth profile. The reason there are GT, GT2, and GT3 products is because there have been changes in the construction of the belts and sprockets over the years. For example, Gates is now selling the third generation of PowerGrip belts with the GT tooth profile. That product line's corresponding sprockets are on their second generation. That's why PowerGrip GT3 belts are used in PowerGrip GT2 sprockets.
This applies to Poly Chain components as well. Poly Chain GT and Poly Chain GT2 belts had aramid tensile cords. The current third generation of Poly Chain belts use carbon tensile cords, hence the product line name "Poly Chain GT Carbon". The sprockets are currently on their second generation which is why Poly Chain GT Carbon belts are used in Poly Chain GT2 sprockets.