Looks like the army is testing some improved 8x8 variants. The assault gun variant features a new ramp door, significantly upgraded appliqué armor all around the chassis and turret, revised propeller shrouds. Another variant (4th photo) features a RWS/unmanned turret, but the chassis remains unchanged.
This last photo is blurry, but it appears to show a 6x6 and an 8x8 chassis, with both possibly being command and control variants. It's difficult to judge if they are based on the same 8x8 IFV chassis (shown in the first four photos), or if they are based on the smaller Brave Warrior (Humvee-sized) platform.