The front sway bar looks quite thick, and it also has a strange round portion in the middle. It looks a bit like the active stabilizer bars used on various Land Rover and BMW products. On the road, these systems can keep the sway bar nice and stiff, but then soften it up off-road for a potentially more comfortable ride, and to possibly gain a bit more wheel travel.
There's also the possibility that it's a sway-bar disconnect like what's used on the Wrangler Rubicon and the Ram 2500 Power Wagon. While those systems provide a lot of benefit for solid-axle vehicles, the Bronco clearly has independent front suspension like its Ranger cousin, so this seems less likely.
Another tidbit worth discussing: the Bronco's tires. Our spy photographer got close enough to get a clear shot of the size, and we can see the prototype wears 285/70R17 all-terrain tires, which comes out to roughly 33 inches. Those are the same size as on both the Ranger Raptor and the new Wrangler Rubicon, and are bigger than the roughly 30-inch tires available on the Ranger FX4. All in all, the Bronco is shaping up to be a pretty serious off-roader.