"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Apple Seeds Fourth Beta of iOS 10.2.1 to Developers and Public Beta Testers
Registered developers can download the fourth iOS 10.2.1 beta from the Apple Developer Center or over-the-air with the proper configuration profile installed.
It isn't yet known what features are included in iOS 10.2.1, but as a minor 10.2.x update, it appears to focus on bug fixes and performance improvements rather than major outward-facing changes. No new features were discovered in the first three iOS 10.2.1 betas, but we'll update this post if any changes are found in the fourth beta.
iOS 10.2.1 follows the release of iOS 10.2, a significant update that brought Unicode 9 emoji, a new TV app, Messages Screen Effects, Music improvements, and a whole slew of bug fixes.