"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Snow Leopard Build 10A421 Seeded to Developers
As usual, Apple provides few hints about changes in the new build, although users with access to the new version will certainly be examining the update to look for any modifications.
This Snow Leopard Developer Preview Update is recommended for all users running the Snow Leopard Developer Preview Build 10A411 or later. This update includes general operating system fixes for stability, compatibility, and security.OS X Snow Leopard is slated for a September release and will cost $29 for current OS X Leopard owners. Users purchasing a new Mac on June 8th, 2009 or later can receive the updated operating system for $9.95 though Apple's "Up to Date" program.