Apple has released new iOS 18 firmware for the AirPods Pro 2 (both Lightning and USB-C)and AirPods 4 (with and without ANC). It is not clear yet what this firmware does; it could be simply bug fixes, or it could be necessary code to enable the new hearing features coming soon with iOS 18.
The firmware version for the AirPods Pro 2 is 7A302 and AirPods 4 get firmware version 7A304, up from 7A294. Apple has not yet issued release notes for this update, but when it does it can be found here.
There isn’t a way to force an upgrade to the new firmware; it will automatically install when the AirPods are in their case and charging. It can take hours or even days to get the latest firmware. If you haven’t used your AirPods in a long time, taking them out of their case and using them for a few minutes before putting them back in and on the charger may help speed things up.
To see what firmware version your AirPods are running, you can open the Settings app, select your connected AirPods (near the top), scroll down past all the options to the About section, and look at the Version line. You can also find this information in General > About > [name of your AirPods].