@User: The difference in the position of the metal stack (with metal2 and everything above raised to make room for the ReRAM layers) made it necessary to split out the ReRAM support as a separate PDK. The differences are minimal and really only affect parasitic capacitances and resistances in the upper metal layers. But in principle, a design spec'd to sky130A could fail if manufactured in sky130B, or vice versa, although such a scenario is unlikely. All Open MPW runs from MPW-four and up will have ReRAM support and therefore will be sky130B (MPW-four itself is a special case because we are splitting the lot so that half of it is effectively sky130A and the other half sky130B).