The STeG 4 is a light armored vehicle produced on the factory world Urdesh. The meaning of STeG remained kind of a mystery, it is obviously an acronym, some being more creative than others, presumed it to stand for Standard Template Ground vehicle pattern 4, which would actually fit in quite nicely all said and done. As you know, the STeG 4 resembles an armored car similiar to that of the Tauros (Meaning it would be one of the few wheeled vehicles of the Imperium) and it would be considered a potent vehicle for Planetary Defense Forces as their analogue of the Imperial Guard's Chimera. Though out of universe, the name is rather reminiscent of the widely produced STuG assault guns made by Germany in the second world war which while the second most frequently built German armoured vehicles; got overshadowed by the flashier panzers even though the late war panzers are almost universally agreed to be overdesigned, ridiculously overcosted, overweighted, maintenance hungry, incredibly resource inefficient pieces of shit while almost nobody has anything bad to say about the STuG III and IV. That being said, its configuration makes it close to the AMX-10 RC in that its a lightly armored reconnaissance vehicle armed with a large cannon that you wouldn't normally find on such a vehicle.
Whilst the vehicle was originally meant for either PDFs or backwater Guard regiments, its capture by the Blood Pact has made it invaluable due to being used as a reconnaissance and patrol vehicle. In combat situations, it often provides immediate heavy weapons fire support to infantry squads; it is also frequently an escort vehicle for supply convoys.
These wheeled vehicles have three axles and are fast and flexible. The main armament is a 40mm cannon in a turret. If the STeGs are armed with armor-piercing ammunition, their high rate of fire can make them even more dangerous for heavier tanks. Handy for dealing with Sentinels, rushing artillery positions, playing pocket-Predator, etc.
Being an armored car, it is of no surprise that the STeG 4 is larger than the dune buggies known as the Tauros, thus it is safe to assume that they would resemble something akin to a Goliath Truck. Being far more armored and armed as well as carrying a larger compartment of troops. Basically an Imperial/Chaos Humvee of sorts.
When Urdesh was conquered by chaos troops during the Sabbath Crusade , many vehicles fell into the hands of the enemy. Since then, the factories have been tirelessly producing new vehicles for the Chaos followers, and have been widely used as supportive elements of the Blood Pact.