To be frank, the Nexus 5 and Nexus 7 which are Google’s Developer devices were not supposed to get another Android L update before the official and final release. Google has been very generous and overridden what they had said. The search giant has made the new updated Android L developer preview images available for download for all their Nexus 5 and Nexus 7 users. There is no change-log yet but confirmation exists that the update contains good support for Android Wear.
Android L was revealed at the Google I/O earlier this year in San Francisco and was released as a preview a few days later. There are strong speculations that the Android L update will be released with the next line of Nexus devices. Apart from all hear and say, there are rumors that the company is working on a Nexus tablet which is supposed to feature a Nvidia 64-bit processor. So, you can take out one conclusion from this, that the release is expected sometime in October 2014 when the devices will be launched.
The Developer Preview users have not yet reported anything serious with respect to this build because this update is not very old having a build date only a couple days after the original one.
Source : Google