There is an unofficial Android 6.0 CM 13 custom ROM build available for all the Sprint Galaxy S3 users. If you want to install this new custom ROM on your phone, then you should check the instructions in this post.

The Unofficial CM 13 Android 6.0 ROM is based on the AOSP Marshmallow releases, and despite the fact that it isn't an official CM 13 release it still offers a stable and reliable OS experience. Before installing this new custom ROM on your device it would be great if you would take a look at the preparation steps below, as you will need to make sure that your Sprint Galaxy S3 phone supports installation and that you won't be skipping any steps.

Here are the guidelines that you need to take into consideration before starting the Unofficial CM 13 flashing process for Sprint Galaxy S3.

Use this tutorial only with the Sprint version of the Samsung Galaxy S3 smartphones. Don't try to update any other devices with the files that you will find in this post.

Your smartphone has to be rooted and it should the latest build of a custom Recovery based on the popular CWM or TWRP Recovery images. Make sure that the installed custom Recovery is updated to its latest version, so that it supports the new Android 6.0 custom ROM installations.

In the tutorial you will find two additional preparation steps like the NANDROID Backup and the Factory Reset ones. The NANDROID Backup creates a full restore point for your device, one that can be used in case the new ROM doesn't boot in normal mode.

The Factory Reset step will remove the old custom ROM and allow Unofficial CM 13 ROM to boot in normal mode successfully. Factory Resetting your phone will remove all the data from system partition, but it won't delete any files from internal storage.

If you need to save any data from installed applications, then you can use Helium tool for Android.

This is a guide that you should only use in case you are an advanced user, we cannot be blamed in case you brick the phone nor in case you lose any data files in the process.

Check the battery charge level of your phone before beginning the update, it should be over 50%, so that your device won't switch off during the installation process.

How to install Unofficial CM13 Android 6.0 ROM for Sprint Galaxy S3:

  1. Download the Unofficial CM 13 Nightly zip from here.
  2. Download Gapps for CM13 ROMs from here.
  3. You have to move both zip files directly to your phone's internal storage.
    - do not unzip the files.
    - disconnect your S3 from PC after the files are copied successfully.
  4. Power off your phone and then boot it in Custom Recovery Mode.
    - remember that both CWM and TWRP latest Recovery builds will work with this post.
  5. Create a NANDROID Backup for the ROM that is already installed on your device.
    - this file can be used in case the new ROM doesn't boot in normal mode.
    - for CWM-based Recovery select 'backup and restore' option.
    - for TWRP Recovery select 'backup' option.
    - set a name for the file and confirm process.
  6. Now you can factory reset your device:
    - CWM: select 'wipe data/ factory reset'.
    - TWRP: select 'wipe' options.
    - confirm.
  7. Start the Android 6.0.1 custom ROM installation:
    - for CWM select 'install zip from sdcard', then 'choose zip from sdcard'.
    - TWRP: select 'install'.
  8. Find the Unofficial CM 13 zip file and confirm its installation process.
  9. After the custom ROM is installed you will need to flash the Gapps zip files, too.
  10. Reboot your phone in normal mode when all the new files are installed successfully.

NOTE: the first boot process of this new custom ROM i going to take a while before it completes.

If you need any extra help completing the update, then you should tell us in comments.

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