The Android M Developer Preview was launched by Google at the end of May, after the official unveiling of the most important new features in the latest OS release. Back then, Google promised that the M Developer Preview would receive a couple of updates before the software becomes stable enough to be consumed by the general public. These updates were supposed to hit roughly at the end of June and at the end of July.
It's a bit late by that time frame, but the first update to the Android M Developer Preview is now out. You can either grab one of the new system images from the developer preview website and manually install, or wait for your device to notify you about the new bits.
In a first for Google, this time around the preview comes with over-the-air updates enabled. The company estimates that all the devices which currently have the original preview image installed should receive the update within a few days.
The preview can still only be installed on the LG Nexus 5, Motorola Nexus 6, HTC Nexus 9, and Asus Nexus Player. The update contains fixes based on developer feedback. It comes with the up-to-date M release platform code, as well as near-final APIs. The full changelog is available at the Source link below.
The final release of Android M will become available sometime this fall, just as initially planned.