"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Apple Issues Software Update to Mountain Lion Developer Preview 4
This update is the second time Apple has updated the Mountain Lion Developer Preview via the Mac App Store rather than releasing an entirely new DP -- Apple issued a similar update in May.
Apple did not specify changes in the update, saying only that it "is recommended for all users running OS X Mountain Lion Developer Preview 4. With Mountain Lion's final release expected next month, Apple should be moving towards a final build soon.
Among other things, the update adds support for more Facebook notifications and PowerNap support for supported machines. It weighs in at 1.08GB and has a build number of 12A248, up from 12A239 previously.