We report 55-nm gate AlInN/GaN high-electron-mobility transistors (HEMTs) featuring a short-circuit current gain cutoff frequency of f(T) = 205 GHz at room temperature, a new record for GaN-based HEMTs. The devices source a maximum current density of 2.3 A/mm at V-GS = 0 V and show a measured transconductance of 575 mS/mm, which is the highest value reported to date for nonrecessed gate nitride HEMTs. Comparison to state-of-the-art thin-barrier AlGaN/GaN HEMTs suggests that AlInN/GaN devices benefit from an advantageous channel velocity under high-field transport conditions.