As noted by MacRumors, Apple has released new firmware updates for the second-generation AirPods, the AirPods Pro, and the AirPods Max.
All three of the models are now running 4A400 firmware, up from 3E751 for the standard AirPods, 3E756 for the AirPods Max, and 3E751 for the AirPods Pro. There’s no standard way to upgrade the AirPods software, but firmware is generally installed over-the-air while the AirPods are connected to an iOS device.
Putting the AirPods in the case, connecting the AirPods to a power source, and then pairing the AirPods to an iPhone or an iPad should force the update after a short period of time. However, you can check your AirPods or AirPods Pro firmware by following these steps.