How to Update AT&T One A9 to Android 6.0 Marshmallow using BASE ROM

As there is no news from the manufacturer or Google to update AT&T HTC One A9 to latest Android 6.0 Marshmallow. So, there must be users who will like to taste of Android Marshmallow on their HTC device. This article is for those users who are eager to update their device to Android Marshmallow by any means. HTC One A9 AT&T variant can now be updated to Android Marshmallow via BASE custom ROM.HTC One A9


This ROM has all the features of the official Android Marshmallow and the ROM works fine in its initial stage. But there may be few bugs which will not allow some of the ROM functions to work properly.

Moreover to install this ROM on your device you need to have root access and custom recovery installed on it. It must also noted that if you flash this custom ROM your device warranty will be void.

So, after knowing all this facts users who like to flash this ROM can go ahead and follow the below mentioned steps.

Preparing Your Phone

  • This instructions are for AT&T HTC One A9 only, do not attempt to try it on other devices.
  • Phone should be fully charged to prevent interruption during process.
  • Back up the useful data and also make Nandroid back up of current ROM.
  • Install the USB drivers for phone on computer if not installed already.
  • Device should be rooted and bootloader unlocked.
  • Custom recovery like TWRP or CWM must be installed on it.
  • Enable USB debugging mode though Settings > Developer options > USB debugging mode.USB Debugging

Procedure to update AT&T HTC One A9 to Android 6.0 Marshmallow via BASE ROM

Follow the process mentioned below –

  1. Download the Android 6.0 Marshmallow BASE ROM file from the link.
  2. Download Google App’s for Android 6.0 file from here (download if required).
  3. Copy the files to phones internal storage memory through USB cable.
  4. Switch off the phone and Reboot into recovery mode(Press and hold Home button, Power button and Volume Up key till logo appears).
  5. Backup the data in recovery mode by selecting Backup/Restore option.How to reboot from recovery mode
  6. After finishing Data backup perform WipeData/Factory Reset function from the menu (Use volume keys to navigate between options and home button to select the option) .factory reset
  7. In the main recovery menu select Install Zip from SD card.
  8. Select Choose Zip from SD card (Use volume keys to navigate and home button to select the file).
  9. Repeat the Step 8 for Installing Google app’s if necessary.
  10. Return to the recovery menu and click on Reboot system Now.
  11. Wait till the process completes.

NOTE:First reboot may take several minutes to complete, please do not panic and let the process complete.

Congrats your AT&T HTC One A9 is now running Android 6.0 Marshmallow, check the status in Settings > About phone.