Update: Looks like the Nexus 6, 9 and Nexus Player are also able to be enrolled now.
Google surprised us all this morning, dropping Android N factory images for selected Nexus devices, but they’ve also announced a new way to get the developer previews via an OTA update. That program has just kicked off and you can now register your Pixel C, or Nexus 5X/6P to get an OTA update to Android N.
The Android Beta program has just kicked off at g.co/androidbeta where once you sign in with your Google account you can register your device to receive the OTA update to Android N. The update brings all the features of the Android N developer preview, but also take your chances with any bugs. Google intends to release regular updates for the devices, but still, it may not be worth the risk on your daily driver.
On the page, Google also explains a little about how the Beta Program will work:
The Android Beta Program gives developers an opportunity to try out pre-release versions of Android. The program is currently targeted towards developers and is not suitable for use on your primary device (see known issues).
Devices that you opt into the program will receive an over-the-air (OTA) update to the latest beta version of Android N. The updates that you’ll receive as a part of this program are unstable pre-release versions, and may contain errors and defects that affect your device.
You may remain in the Android Beta Program beyond the N release to preview future Android N maintenance releases (MRs). If you choose to do so, you will automatically get an OTA update to pre-release versions of the MRs as they become available. At the end of the program, you will begin to receive regular public updates.
You may opt-out of the program at any time to return to the stable, public version of Android. Note: If you opt-out when your device is running a beta version of Android, all user data on the device will be wiped.
If you want to update your device, head over to g.co/androidbeta, sign in and register your device.