The worldwide Greek yogurt market is a growing multi-billion dollar industry in need of a solution for its environmentally problematic acid whey (GAW) byproduct. Utilization of supercritical fluid extrusion (SCFX) technology presents the opportunity to convert GAW into value-added and high-protein sweet and savory snack foods that will resonate with today’s market. Additionally, hydrolysis of the lactose in GAW prior to extrusion has the potential to polymerize into galactooligosaccharides (GOS) under the high temperature, pressure, and shear conditions, transforming lactose into a source of dietary fiber. This study evaluated the effects of concentrated 12 ˚Bx Greek acid whey substituted in lieu of water during the extrusion of milk protein concentrate-based snacks. Water, unhydrolyzed GAW, and hydrolyzed GAW were used as the three liquid sources during extrusion and physicochemical, textural, and sensory properties of the extrudates were evaluated. Addition of GAW significantly (P < 0.05) increased extrudate radial expansion ratio and porosity and decreased piece density. GAW generally improved textural characteristics of hardness, crispness, and crunchiness or produced extrudates comparable to commercial products. A consumer sensory acceptance test showed that GAW significantly improved hedonic and JAR scores in all four attribute categories. GOS content was analyzed and found to be 2.5% tetrasaccharides and 0.9% trisaccharides in the sweet formulation with hydrolyzed GAW. The results indicate GAW’s potential to replace water during extrusion, simultaneously utilizing an environmentally undesirable byproduct while improving extruded snack foods.