How long do smart CO detectors actually last?

UL 2034 5th Edition sensors are rated for roughly 10 years from the date of manufacture, and r/smarthome and r/firealarms commenters repeatedly remind buyers that the whole unit must be replaced at that point regardless of battery state. Battery-backup models typically need fresh AAs every 1-2 years, and chirping complaints in r/homeowners threads almost always trace back to either a weak backup battery or an end-of-life sensor.