If you feel like being brave (and have a second phone on hand, just in case), you can now download the preview versions of Android L Release for the Nexus 5 and Nexus 7 (2013).
According to Google, “[the] image is not a stable release, and may contain errors and defects that can result in damage to your computer systems, devices, and data. The preview Android system image is not subject to the same testing as the factory OS and can cause your phone and installed services and applications to stop working.” In other words, things will break.
It’s worth mentioning that many user-facing features are either not finished, or not optimized for current apps, too. This is the first time Google has released a preview version of an upcoming Android release, which indicates that the implications for L are larger for the company’s entire development platform than ever before.
As the preview release is a factory image, it will wipe your Nexus device to factory settings, so before following the installation instructions make sure to back up your important apps and data.