Not an earlier model....just a new look. DC is out nation's capitol, so it wouldn't make much sense for all of the robots in DC to be outdated. I think Bethesda gave the sentry bot a new look/made them stronger because of those dog-ugly securitrons from NV, which were somehow stronger than sentry bots. This new look, though is so horrible. It's not just them, Fallout 4 in general has an ugly art style compared to 3 and NV. Sure, the sentry bots are bigger, but the old ones look much more badass to me :sad: