This was the first model in the GSX400 series and served as the inspiration for the GS400E-2, which was the final model in the GS400 series. Its 400 cm³ 4-stroke 2-cylinder DOHC engine generates maximum horsepower of 44 PS and maximum torque of 36.28 N·m due to the adoption of Twin Swirl Combustion Chambers (TSCCs). The GSX400E and 750E were the first models in the world to adopt the Anti Nose Dive Forks (ANDF) proven via the RGB500 Grand Prix racer. Double front disc brakes and low profile tires were adopted in a subsequent minor model change in 1981.

This model combines a wholly new exterior design with the 400 cm³ 4-stroke 2-cylinder DOHC engine with Twin Swirl Combustion Chambers (TSCCs), 6-speed transmission, frame, and Anti Nose Dive Fork (ANDF) system adopted on the GSX400E. The result is a 400 cm³ model for Japan with styling that incorporates the lines of the KATANA series. The 16-liter fuel tank capacity makes this model particularly suited for long-distance riding.

The design of this model is based on the GSX1100S KATANA, whose popularity had remained unchanged since its debut in 1981. While remaining true to the original design, the GSX400S incorporates the latest technologies in both the engine and the chassis. The 4-stroke liquid-cooled 4-cylinder DOHC engine was newly engineered to emphasize torque, and tuned for optimum performance in the low- to mid-rpm ranges to prioritize rideability on city streets. Despite the liquid-cooled configuration of the engine, cooling fins inspired from air-cooled designs were added to the cylinder head and cylinders to create dynamic and memorable styling. The GSX400S KATANA also features a rear suspension equipped with a reservoir tank, large disc brakes, and wide tires to deliver both stable braking force and riding performance.