From Apple’s Upgrade to the new Home architecture support page after iOS 16.4 shipped:
Learn how to upgrade to the new, more reliable, and more efficient Home architecture.
How, uh, exciting? I’m usually not one to wait on upgrades, but I did dodge the original bullet from when this change first shipped with iOS 16.2 and was quickly pulled after many reports of HomeKit devices that were left with connection issues. Or in other words: exactly what this was supposed to fix.
As of now I will probably let this one sit a little while before upgrading only because there’s a lot of potential for things to go wrong, family members to be annoyed, and very little upside for the keeper of the smart home—me. Frankly, Apple has done a terrible job explaining what the differences are and why this is even important outside of vague claims about reliability and efficiency. The best explanation I could find was via HomeKit Helper:
So how is the New Architecture more efficient and stable? With previous versions of HomeKit, your HomeKit “controller” (the Home app on an iPhone, iPad, or Mac, for example) talked directly to each device in your home. The state of a device is not updated in the background, which is why when you open the Home app, devices say “Updating…” for awhile; the Home app is literally asking every device in your home for its current status. The more devices you have, the longer it can take.
In the New HomeKit Architecture, ALL HomeKit requests are serviced by the HomeKit Hub. Your Home app no longer need to query each device individually. The HomeKit Hub is continually maintaining an up-to-date status of each device and simply passes that information to the Home app. This should virtually eliminate the “Updating…” issue since current status of every device is always immediately available and should result in a much better user experience.
I plan on playing it safe and making sure all the smart devices around the house get their latest firmware upgrades applied before I try this out.
Update from May 8, 2023: I performed the upgrade last week and it was a total non-issue. Haven’t noticed any improvements, but everything is still responding and connected.