The objective of the HX concept car project was to potentially market a Hummer branded vehicle in the smaller-sized and lower priced SUV market segments. Development of the vehicle, dubbed H4, began in 2004 and the new model was to be Jeep Wrangler sized.
The 2008 HX show car was smaller than both the H2 and H3. It featured a 3.6 L (220 cu in) V6 engine mated to a six-speed automatic transmission. The HX shared with other Hummers a body-on-frame design, with front and rear independent suspensions, four-wheel-disc brakes, and full-time four-wheel drive.
The HX was shown with a slant-back configuration, wearing a desert-inspired matte olive paint scheme, and featured removable doors with exposed hinge pins and removable composite fender flares that are attached with quarter-turn quick-release fasteners.
The exterior's matte olive color was also applied to the interior's largely sheet metal-covered panels. The floor was a rubberized material. The HX seats four, with a pair of bucket-type seats in the second row. The rear seats are removable to allow cargo room. The console included a compartment for phones and MP3 players with no conventional radio, only integrated speakers and a connector for digital players or similar devices.
Three designers, recent graduates of College for Creative Studies who were new to General Motors, Robert Jablonski, Kang Min-young, a South Korea native, and David Rojas, a native of Peru, participated in the development of the Hummer HX.