Here are pages I found for the

2016 Quick 4

2018 Quick 8

Looks like Quick 4 is a pricier, better-specced bike than the Quick 8, even at 2yr old.

Reasons to get the Quick 4: 3x8 instead of 3x7 gearing (or is it even 3x9?), carbon instead of steel fork, nice schwalbe tires, lighter 24spoke wheels

Reasons to get the Quick 8: if you are heavy (>200lb?) then 32-spoke wheels will be stronger. The updated frame, or the color looks better (subjective).