As Maris said, replenished Xtol seems to last almost forever, even in the old hard rubber Kodak floating lid tanks. I have been using it well over 10 years both as replenished and one-shot and have never had it expire. That said, I mix it with distilled water and store it in brown glass bottles. I use the same mixing and storage for all developers, including D23, and have not had a problem with chemistry expiring.