"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Apple Seeds Fourth Beta of iOS 12.1.3 to Developers and Public Beta Testers
Registered developers can download the new iOS 12.1.3 beta from Apple's Developer Center or over-the-air once the proper configuration profile has been installed from the Developer Center, while public beta testers can get the beta over-the-air.
The fourth iOS 12.1.3 beta is technically the third beta, but because iOS 12.1.3 includes the same updates that were supposed to be included in the iOS 12.1.2 beta that was already released, Apple released the initial iOS 12.1.3 as a second beta rather than a first beta.
Apple seeded just one beta of iOS 12.1.2 before tweaking the software to include some emergency bug fixes and the aforementioned software changes in China, rushing the update out and pushing content originally planned for iOS 12.1.2 to iOS 12.1.3 instead.
iOS 12.1.3 will mark the fourth update to iOS 12. We don't yet know what features are included, and no major changes have been found in the iOS 12.1.3 betas we've received thus far. If we find anything new in the fourth iOS 12.1.3 beta, we'll update this post.