The G.91 Y was a multi-role fighter which first debuted in 1966. Based largely on earlier Fiat G.91 fighters, the G.91 Y was a complete redesign but kept the basic shape of the G.91 series. The biggest difference between the two types was the conversion from a single-engine to two General Electric J85 turbojets outfitted with afterburners. This conversion alone resulted in a 60% increase in the aircraft's thrust, however, it was not enough for this jet to become supersonic even when in a dive. The new design of the aircraft was based on the longer trainer version of the G.91 which allowed the installation of the bigger engines. The armament was also improved with the addition of two DEFA 30mm cannons, and all the G.91 Y aircraft served only with the Italian Air Force.

It was introduced in Update "Drone Age". The G.91 Y is a radical modernization of the original G.91, with the addition of two powerful engines in a bigger airframe, the aircraft behaves differently when compared to the lighter and more agile G.91 R/4 as an example, but this comes with the benefit of a higher top speed, and a much better energy retention and acceleration, problems that were very big in earlier G.91s. The aircraft lacks countermeasures or any kind of IR guided missiles however, and it relies on its improved cannons and AA-20 Nords for air combat. For ground battles it is capable of carrying more rockets, bombs and the AS-30 Nord, which has more range, and a bigger payload, but the same MACLOS guidance compared to the AS-20.