Splitboarding boots are not drastically different from their softboot counterpart, but the few key differences do add up to improved performance and comfort when out in the backcountry.
First, splitboarding boots offer negative flex when striding out on the skin track, which equates to improved touring efficiency on long, low angled approaches.
Secondly, splitboard boots possess a rigid, dense rubber mountaineering sole that will take a semi-auto crampon so you can bite and purchase firm snow in mountaineering applications. In addition, the toe box is fairly rigid so you can more effectively kick in steps during a boot pack.
Lastly, some boot models offer more variable closure systems so you can dial in and customize the fit and comfort depending on your mode of travel at the moment.