Introduces bar-headed goose hemoglobin variants that bind oxygen with extraordinary efficiency, combined with enhanced lung surfactant production and expanded alveolar surface area. The user's blood carries 40–60% more oxygen per volume than unmodified human blood, and the lungs extract oxygen from air with dramatically improved efficiency. The result is superhuman endurance — the user can sustain aerobic activity far beyond normal human limits, recover from exertion in minutes rather than hours, and function normally in thin atmosphere that would leave an unmodified person gasping. The blood itself is noticeably darker red than normal — in some installations, it's almost black from the density of hemoglobin. Crucible Genomics developed this modification for high-altitude industrial workers but it has found its way into every tier of society that values physical endurance.