"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Apple Seeds First Beta of macOS High Sierra 10.13.3 to Developers [Update: Public Beta Available]
The macOS High Sierra 10.13.3 beta can be downloaded from the Apple Developer Center or through the Software Update mechanism in the Mac App Store with the proper profile installed.
It's not yet clear what improvements the third update to macOS High Sierra will bring, but it's likely to include bug fixes and performance improvements for issues that weren't addressed in macOS High Sierra 10.13.2.
The previous macOS High Sierra 10.13.2 update focused solely on security fixes and performance improvements, with no outward-facing changes introduced.
Update: Apple has also seeded the macOS High Sierra 10.13.3 update to public beta testers.