New HomeKit Architecture
With the advent of Matter support in HomeKit in iOS 16, Apple also announced an improved HomeKit architecture that would make things faster and more reliable, particularly in larger homes with lots of devices.
The new architecture appeared in iOS 16.2 betas, but was pulled before the final release, likely due to not being quite ready for prime time. Now, Apple has (hopefully) fixed whatever was wrong and reintroduced it for general consumption in iOS 16.4.
For now at least, the new architecture is optional. Should you wish to try it out, though, you’ll need to ensure that all of your devices with access to your home are running iOS 16.4 or its equivalents for the iPad, HomePod, and Apple TV.