"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Apple Seeds Third OS X 10.11.4 El Capitan Beta to Developers
The third OS X 10.11.4 beta can be downloaded through the Apple Developer Center or via the Software Update Mechanism in the Mac App Store.
OS X 10.11.4 offers a couple of new features, such as the ability to support password protected notes in the Notes app, but like the recent OS X 10.11.3 update, it appears to focus primarily on under-the-hood bug fixes and performance improvements with few noticeable outward-facing changes. Almost all of Apple’s OS X updates to date have been smaller updates that improve performance rather than introduce new features.
We’ll update this post with any features or significant changes that are discovered in the third beta of OS X 10.11.4.