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Update AT&T Galaxy S3 to Android 6.0 Marshmallow via CyanogenMod 13 ROM

AT&T Galaxy S3 is one of among those lucky device that received the latest Google’s Android OS Marshmallow 6.0 firmware update. This update is available for the international variants of this handset. Samsung may not release the Android M software for Galaxy S3 but still you can update your phone and enjoy the latest Android OS experience by installing the unofficial CyanogenMod 13 ROM which has been ported to the US variant of the Galaxy S3. This CM13 custom ROM is based on Android 6.0 Marshmallow which has been build from the CM 13 sources available On github. As this ROM is in its early stages thus you might face some minor bugs but the initial build comes with network fixes and it is expected that the found bugs will be fixed in future releases.

So if you are interested to get the Android 6.0 Marshmallow CM13 ROM on your AT&T Galaxy S3 then go ahead and follow the given steps. Keep in mind that this is a custom ROM which is not officially released by Samsung, thus you’ll need the latest version of a custom recovery like TWRP or CWM in order to install the ROM and Gapps .zip files on your phone. In this guide, first we’ll flash the ROM and the given Google Apps package (Marshmallow compatible). Take a look on the bugs reported by users. You can also read more here to know about further CM 13 updates.

Flash AT&T Galaxy S3 on Android 6.0 Marshmallow with CM 13 ROM

Note Working:

  • This is a preview build, may not serve as a daily driver.
  • Network has been fixed and some other functions may not work.


This guide containing the Android 6.0 CM13 custom ROM is compatible with AT&T Samsung Galaxy S3. Do not try to install this firmware on any other device or incorrect variant. Check the model number of your device first.


AndroidBlog will not be held responsible for any kind of damage occurred to your AT&T Galaxy S3 during or after the installation of this CM13 Android 6.0 custom ROM. Rooting or installing a custom ROM will void the warranty of your device. Proceed at your own risk.


  • It is highly recommended to take a proper back up of your important data and settings on the phone using a custom recovery such as CWM or TWRP. In case anything goes wrong then you’ll be able to restore your data.
  • Download and install proper USB Drivers for the Galaxy S3 on PC.
  • Enable USB Debugging Mode on Galaxy S3 from Settings > Developer Options.
  • The latest version of a custom recovery like TWRP should be installed on it.
  • Make sure that the battery level of your Galaxy S3 is at least about 80% before proceeding to the installation guide.

Required Files:

Steps to Update AT&T Galaxy S3 to Android 6.0 Marshmallow using CM13 Custom ROM:

1:- Download the Android 6.0 Marshmallow CM13 ( and Google Apps package ( from the above links on your PC (probably on the desktop).

2:- Now, connect the AT&T Galaxy S3 to the PC using its USB data cable.

3:- Move the CM13 ROM zipped file to the internal storage of your phone.

4:- Now, disconnect the device from the PC and turn it OFF in order to boot into Recovery Mode.

5:- Turn ON the Galaxy S3 while pressing and holding Volume Down + Power buttons altogether for a while until the device enters into Recovery Mode.

6:- While your device is now in recovery mode, it is recommended to perform a nandroid backup and select all the partitions including System, Data, Boot, Recovery, EFS.

7:- Once the backup is completed, perform a full wipe.

8:- Go back to the main menu of TWRP recovery and tap the wipe button, select Advanced Wipe and after that select Dalvik CacheSystemData, and Cache. Confirm to wipe.

9:- Navigate to the TWRP main menu and tap on the install option. Select the CM13ROM that you have already transferred to the internal memory of your phone and select it.

10:- Proceed to the installation by swiping on the confirmation button.

10:- Repeat the above steps to install Google Apps package on AT&T Galaxy S3.

12:- After the successful installation of ROM and Google Apps, select “Reboot System” in the recovery.

Your Galaxy S3 might take about 4 to 5 minutes to boot for the first time after installation.

Done! You have successfully installed the latest Android 6.0 Marshmallow with CyanogenMod 13 custom ROM on AT&T Galaxy S3.

Aamir Jamal

An Android Geek and audiophile who love to read and write reviews/tutorials about gadgets and new tech stuff. He has written 1007 guides and other posts.

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