How long should a pair of gaiters last?

It varies wildly by category. Heavier hiking gaiters from Outdoor Research are described in r/CampingandHiking and on trailspace.com as multi-year purchases, sometimes covered by lifetime warranty. Ultralight trail-running gaiters from Altra draw the opposite complaint on r/ultrarunning, with at least one thread flagging fabric failure under 100 miles. Match weight to terrain: the lightest options are not the most durable.