Apple today released its latest updates for iOS, iPadOS, and tvOS. The biggest change in iOS 13.5 is the new Exposure Notification API, but there are also other changes like Face ID improvements.
Apple has been testing iOS 13.4.5 with developers since March 31, although with beta 3, it became iOS 13.5. After offering up the GM seed earlier this week, the update is now available.
The reason that the version number changed is because it includes the new Exposure Notification API, which is used for contact tracing. An update like iOS 13.
