"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Apple Seeds Second macOS High Sierra 10.13.1 Beta to Developers and Public Beta Testers
The second macOS High Sierra 10.13.1 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.
macOS High Sierra 10.13.1 appears to focus on bug fixes, performance improvements, security enhancements, and other under-the-hood changes, but it also introduces a range of new Unicode 10 emoji like crazy face, pie, pretzel, t-rex, vampire, exploding head, face vomiting, shushing face, love you gesture, brain, scarf, zebra, giraffe, fortune cookie, pie, hedgehog, and more.
macOS High Sierra is a major update that introduces APFS, a new more modern file system, HEIF and HEVC photo and video encoding improvements for smaller file sizes without compromising quality, Metal 2, and several new features for Safari, like autoplay blocking for videos and Intelligent Tracking Prevention to better protect user privacy.
Update: Apple has also released the second beta of macOS 10.13.1 to public beta testers.