I've decided to upgrade to road tubeless. Hutchinson sells both "Tubeless" and "Tubeless Ready" tires. According to Hutchinson' website, Tubeless Ready means that (in addition to having a special bead) the tire's tread is air permeable and will gradually lose air, so sealant is needed, not just to seal punctures, but to slow the loss of air.
Their Tubeless tires, on this other hand, have a butyl lining that prevents air loss. Although a sealant can be used to seal punctures, it's not required.
My question: Do tubeless tires -- the tires that have a lining -- hold air as well as tires with tubes? (Note, my car's tires don't have tubes and they hold air quite well.) I ask because I need my tires to stay pumped up, and not go soft overnight the way they usually do on my mountain bike.