It's time to fire up those M preview devices again—Google is in the process of rolling out the second M preview build today. The OTA should arrive on all supported Nexus devices that have the first M build in the next few days. If you're the impatient sort, you can grab the system images right now.

The new M preview has a few notable changes, but it's still a developer preview. Some features (like Now on Tap) won't work until the final release. Here's the changelog from Google.

Key changes
  • Permissions changes
    • The android.permission.USE_FINGERPRINT permission now has "normal" protection level, so it is no longer necessary to request this permission directly from the user. The USE_FINGERPRINT permission enables fingerprints to be enabled for authentication, but does not give the requesting app access to the enrollment/fingerprint administration flow.
    • The android.permission.WRITE_EXTERNAL_STORAGE permission has protection level "dangerous", meaning that apps wanting to write to external storage will need to request permission from the user at runtime. Both WRITE_EXTERNAL_STORAGE and WRITE_EXTERNAL_STORAGE are members of the STORAGEpermission group.
    • Remote Bluetooth/Wi-Fi MAC's now require either the android.permission.LOCATION_FINE orandroid.permission.LOCATION_COURSE permission.
    • Some accounts and identity permissions are moved to CONTACTS permissions group and others are removed or granted based on account type. In particular, android.permission.USE_CREDENTIALS,android.permission.MANAGE_ACCOUNTS, and android.permission.AUTHENTICATE_ACCOUNTS are ungrouped pending further changes in a later release.
    • The Wi-Fi permissions android.permission.CHANGE_WIFI_STATE,android.permission.CHANGE_WIMAX_STATE, and android.permission.CHANGE_WIFI_MULTICAST_STATEnow have protection level "normal".
    • The Bluetooth permissions android.permission.BLUETOOTH andandroid.permission.BLUETOOTH_ADMIN now have protection level "normal".
    • Bookmarks and subscribed feeds permissions are removed.
    • Apps included in the system image are no longer granted dangerous permissions automatically. All apps should check for and request permissions at runtime.
    • Introduces the utility method Activity.shouldShowRequestPermissionRationale(String), which lets your app see whether users have previously rejected a permission request. This lets you know that your app should explain the the user why it needs that permission. For more information see the Permissions developer guide.
  • Other changes
    • The android.app.AssistContent and android.app.AssistStructure classes are moved into a new package, android.app.assist.
    • Bluetooth Stylus APIs are updated and include new callback events. TheView.OnStylusButtonPressListener class is renamed to View.OnContextClickListener andGestureDetector.OnStylusButtonPressListener class to GestureDetector.OnContextClickListener.
    • TextInputLayout doesn't set hint for embedded EditText. (fixed issue)
    • Camera Permission issue with Legacy Apps (fixed issue)

Google has also provided a list of known issues with this build, which you can find below.

Known Issues
  • General issues:
    • The system Messenger app crashes on the 64-bit emulator.
    • After updating to Developer Preview 2, Contacts sync experiences intermittent issues. The workaround is to clear and re-sync Contact Storage data after update. To clear data, go to Settings > Apps > Show system > Contacts Storage. Select "Storage" and then Clear data.
    • In YouTube app, it's not possible to share a video. The share window is blank.
    • Android For Work Profile setup is not working properly, so you won't be able to create a new Work Profile after you update. As a workaround, make sure to create the Work Profiles you need in Developer Preview 1 before updating to Developer Preview 2.
  • Issues specific to MPZ79N on Nexus Player:
    • Bluetooth share crashes after clearing data. Please do not clear Bluetooth share data, otherwise you will need to Factory Reset your device
    • There are issues with remote control connectivity. Remote can drop from Bluetooth pairing when left idle.
    • Movies show black screen with some ANRs on exiting the video.
    • In YouTube app, lower-resolution videos have a green bar at the top and some color-ghosting

The updated M preview will have the latest Play Services 7.6 build, and the Nexus player/emulator images have been improved to make validating apps easier.

The Nexus player gets build MPZ79N in this update, but all other devices are MPZ79M. Check the M system image page if you want to manually install it now, otherwise just wait for the OTA. You should get the update on any of the official preview devices that are running the previous build from I/O (MPZ44Q).