Juli Clover, MacRumors:
Apple in July 2021 began offering beta firmware for the AirPods Pro, with the software available for Apple Developer program members.
I don’t recall past AirPods firmware being distributed in this way.
AirPods Pro firmware betas are limited to developers and are quite tricky to install, with an installation guide available below.
Installing the firmware in an unauthorized way can put the AirPods Pro into an unusable state that necessitates an out-of-warranty repair, so non-developers should not attempt to install the software.
And, most importantly:
Apple says that once the AirPods Pro firmware has been installed, it’s important not to put un-updated earbuds into the charging case because they may be updated with the firmware.
This firmware features “FaceTime Spatial Audio and Ambient Noise Reduction”.