Someone on Warseer suggested it looks like an early C20 tractor which the first tanks were based on.
I'm assuming that big wheel is decorative rather than functional? It could be a symbolic wheel of industry?
The skeletal frame, defended by energy fields does fit well with previous descriptions of AM Ordinatus.
They seem to be doing a Steam Punk / Victorian edge to their AM. Not necessarily what I expected, but I think it works well enough and gives them a distinct aesthetic from IG or SM. With shields rather than armour it might not weigh as much as other tanks of it's size and so be faster.
This is a Thallax with Lightning Gun:
It's Lightning Gun (a much smaller version of the gun on the Krios) apparently 'fires an ionizing las-beam down with a powerful phased discharge of electromagnetic force'
I'm guessing / assuming that it's a direct fire weapon and if it's pointing up it's to show that it can and so that it can fire at a titan (I believe the AM are fighting the traitor Tiger Eyes legion in the next book).
The old Horus Heresy collectable card game had an AM vehicle called a Neutrino Irradiator that this is clearly inspired by:
