Actual answer: better ANC. ANC algorithm improvements are one of the more common items I've seen in headphone firmware changelogs. Also, Bluetooth upgrades. I can't remember which, but one of my pairs of headphones gained multipoint support a year or so after release via a software update.
On the Bose 700 headphones there was quite a bit of controversy after many users reported the ANC performance getting worse after an update. This was a few years after the headphones were released, so there were theories of it being intentional degradation to get people to upgrade.
Personally I didn't notice any difference. Bose denied any wrongdoing and seemed to spend real effort on investigating the customer complains.
