Apple has rolled out a new AirPods firmware update with version number 3.5.1 from earlier 3.31. The firmware update seems to come with performance improvements and bug fixes.
The latest firmware update of the AirPods may contain the solution to fix the issue that caused the earphones to disconnect from iPhone randomly during calls. Luckily, it's very easy to update the headphones to the latest software.
How to Update AirPods to the Latest Firmware Version
You don't have to do much to update AirPods to the latest firmware. Make sure to keep the connected iOS device nearby the charging case. Then, simply put the earbuds into the charging case. The headphones will be updated instantly.
Note: Just in case, you are unable to update your AirPods, make sure the case is fully charged. Also, ensure that they have been connected to your iOS device (Settings → Bluetooth). Resetting the charging case may help you in fixing the issue. (You may want to read how to fix the AirPods charging case battery drain issue.)
How to Check AirPods Firmware Version on iPhone and iPad
Once you have updated your AirPods, you can quickly check out the firmware version that's running on the earphones.
Step #1. Make sure that the AirPods are connected to your iOS device.
Step #2. Launch Settings app on your iPhone → Next, tap on General.
Step #3. Now, you need to tap on About.
Step #4. Next up, tap on AirPods.
Step #5. On the next screen, check out the Firmware Version of your AirPods. Also find out the serial number, model number and the hardware version of your AirPods.
Since Apple didn't send any alert or notification that an update for the earphones is available. There is not much clarity about what it features.