According to people familiar with the latest seed, not much has changed from the previous version Developer Preview 6, which was released two weeks ago.
iCloud Keychain is still a work in progress, these people said, as the feature is still listed as a known issue. Developer Preview 6 came with a substantial backend update to the new security feature that required developers to reenable it after installing the operating system.
The latest build also allows for PDFs imported into iBooks while using a previous Mavericks seed to be renamed with Preview. iBooks for Mac was first introduced in Mavericks with Developer Preview 5.
When Apple launches OS X 10.9 Mavericks later this fall, it will come with iBooks, Finder Tabs, Maps, App Nap and Compressed Memory, among other new features.
Developers can download the sixth Mavericks preview via Software Update.