After the Worldwide Developers Conference keynote in June, Apple gave developers a chance to try out the new AirPods models. The version number went from 5A5282d to 5A5304a in the update.
The software can be downloaded from the More Downloads page on Apple's website. If you want to install the beta, you need an Apple product, a Mac, and a AirPods compatible device.
You need to pair the AirPods with an Apple device, connect the phone to a Mac with a cable, and launch the pre-release version of Xcode on the Mac. Once the pre-release testing option is enabled, subsequent updates are delivered over the air.
Improvements to Automatic Switching and bug and stability fixes are included in the latest version of the apple software. After testing is finished, the software will eventually come to all AirPods, and it could be released in the fall along with other operating systems.