Buried within the code of the iOS 16.4 Release Candidate are references to an "A3048" AirPod model and an "A2968" AirPods case haven't been seen before, and it's a mystery as to what they could refer to. The current AirPods 3 and AirPods Pro 2 are only a year and a half old and six months old respectively, so it feels too soon for an upgrade here. There have been claims of Apple working on AirPods Lite, or new AirPods Max, but they're currently thought to be arriving next year.
One other option is that this will be a USB-C version of currently available AirPods or AirPods Pro. With the iPhone 15 rumored to be moving away from Lightning ports later this year, it would follow that Apple would want to ensure its most popular iPhone accessories were similarly updated.
iOS 16.4 Voice Isolation
That's not all the novelties the Release candidate was hiding. There are also some last-minute feature additions, with the biggest of these being Voice Isolation for cell calls (via PhoneArena).
Voice-isolating tech is common on several phone brands' devices, such as Clear Calling on the Pixel 7, and helps reduce background noise while you're talking so the person at the other end can hear you better. This was already a feature for other iOS services like FaceTime and WhatsApp, but Apple look set to bring this to other iPhone phone calls.
Apparently, Voice Isolation isn't enabled by default. It's something you have to turn on in Control Center under Mic Mode while on a call, but it should then stay in by default, going by how it behaves on FaceTime and other apps.
Other assorted fixes brought to us by the Release Candidate include the Photos app Duplicates album now being able to spot repeated photos in albums shared over iCloud, a fix for an Ask to Buy bug on parent devices when child devices request App Store purchases, and another fix for an issue affecting thermostats using the Matter smart home standard.
iOS 16.4 is likely going to be the final major set of additions to iPhones until the iOS 17 beta presumably arrives at WWDC 2023 in a few months. So make sure you're up to speed with the new iOS 16.4 features introduced in the update, including new emoji, more granular always-on display settings and other small improvements to the iOS software.