All cocoa contains caffeine. It’s not an added ingredient. Cocoa may have prebiotic effects though.
By the way, few plant antioxidants actually make it into the blood and have a negligible effect on oxidative stress. I haven’t seen anything specifically on cocoa, but green tea antioxidants end up in the toilet within 2 hours. Oxidative stress also has important roles within the body, like destroying antigens or signalling for repair. If you supplement vitamin C after exercise, for example, your progress will be slower.