"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Apple Seeds Third Beta of macOS High Sierra to Developers
The new beta can be downloaded from the Apple Developer Center or over-the-air using the Software Update mechanism in the Mac App Store.
macOS High Sierra focuses on new core storage, video, and graphics technology, introducing a new Apple File System (APFS), High Efficiency Video Codec (HEVC) and an updated version of Metal with support for VR and external GPUs.
Some apps are also gaining new features. Photos is being updated with a new sidebar that's designed to make it easier to access editing tools and albums, and there are new filters and editing options like Curves and Selective Color. Photos also supports external editing apps like Photoshop and Pixelmator, saving changes made in those apps, and it interfaces with third-party printing services.
Safari is gaining speed enhancements, an option to end autoplay video, and a new feature that puts a stop to data tracking. Siri in macOS High Sierra has expanded music capabilities and a new, more natural voice, and Spotlight supports flight status information. There are also improvements to iCloud, FaceTime, Messages, and Notes.
macOS High Sierra is available for both registered developers and public beta testers, and it's likely a new public beta that's identical to the third developer beta will be released later this week.