The updated 2024 GMC Sierra HD will come in an off-road focused AT4X trim level if this prototype is any indicator.

2024 GMC Sierra HD AT4X – Our Spy Photographer Reports

We caught a dinged-up prototype for the new off-road-focused variant coming with GMC’s 2024 Sierra HD refresh—a prototype believed to be a new AT4X HD model. This latest look gives us our best look yet at the truck’s underbody, giving us our best angle to view the skid plates, and elements of the suspension applied to this very rugged truck. There are many details that suggest that GM is expanding the ZR2/AT4X-spec capability into the HD truck space.

This prototype display’s generous clearances throughout, with a new slim front bumper, exposing a new, beefy front skid plate. There are no low-hanging elements like chin spoilers or wind diffusers, maximizing front clearance and approach angles. The test truck also displays what appears to be a more generous ride-height, with limited obstructions from nose-to-tail.

There are no running boards to aid ingress, but it also looks like the truck could use some rocker guards, as this prototype has taken a beating. There is damage to the rocker panels, a crinkled rear door, and the HD’s integrated step at the start of the box has been bashed upward—signs of some rock-climbing gone awry. A bevy of underbody protection can be seen protecting the mechanical bits under the truck.

This prototype is wearing Goodyear Territory MTs, which are applied to GM’s trucks above the traditional AT4/Trail Boss levels, suggesting that this truck sits above the standard Sierra AT4 HD, and will likely have an AT4X designation. Disguised wheels can’t hide the eight-lug HD set-up.

For now, this is our most revealing look at what’s cooking on GMC’s most off-road-ready HD prototype. We probably need a chance to literally crawl under a prototype to learn all of its secrets—something we hope to happen as testing continues.

For now, this is our most revealing look at what’s cooking on GMC’s most off-road-ready HD prototype. We probably need a chance to literally crawl under a prototype to learn all of its secrets—something we hope to happen as testing continues.