This is not a Sprint Note 4 Marshmallow firmware, but it’s pretty close as far as Marshmallow update goes for the device. The ROM provided below is based on Samsung’s own Android 6.0 code, and thus comes with TouchWiz, as against the AOSP Note 4 ROMs we call unofficial Marshmallow updates.
This requires installation of engineering bootloader and PB5 firmware’s baseband to work properly. So, to install it alright, you first need to install these two before flashing the ROM with TWRP recovery (your TWRP will remain installed, BTW, as it won’t be replaced by stock recovery).
If you ever wish to downgrade back to Android 5.1.1 Lollipop, you can do so easily by flashing the Sprint Note 4 firmware Lollipop version. But, what is must is installing the OK1 firmware’s bootloader (download here), and optionally OK1 baseband (download here) to go back to 5.1.1 alright.
This is really interesting. Samsung is busy update Galaxy S6, S6 Edge and Edge Plus to Marshmallow, while it has already updated Note 5 to 6.0. Next in line are probably Note 4 and Galaxy S5, but it would take some time for the carrier devices to get the udpate.
Hence the proper official Android 6.0 update for Sprint Note 4 is at least a month away. But you get to play with the Marshmallow update already thanks to this leaked ROM. Have fun!
- Lollipop (to downgrade, not otherwise)
How to install
Well, first of all, know that this will trip KNOX, and hence warranty fo your device will be void.
Next, make appropriate backups.
Now install TWRP recovery on your Sprint Note 4. When done, download the Marshmallow files from above and transfer the ROM file to the device.
Using TWRP, do a factory reset, and then install the ROM file. But don’t reboot normally. Instead, choose bootloader option in Reboot menu to boot into download mode.
Now, using Odin, flash the PB5 bootloader on your device, with auto reboot NOT ticked. This is to prevent device to boot normally.
Reboot into download mode again manually (press and hold Volume Down + Home + Power together until your device reboots into download mode). Now, install the PB5 baseband, with ‘auto reboot’ ticked this time around to allow device to reboot automatically after flashing the bootloader.
Upon reboot, your Sprint Note 4 would be running Marshmallow like a boss.
How to Root
Well, simply install the SuperSU 2.68 from here, using TWRP install menu.
How to downgrade to Lollipop
Download the Lollipop firmware, OK1 baseband and OK1 bootloader from above, and install the firmware first of all using Odin (keep auto reboot NOT ticked). Next, install the OK1 bootloader (auto reboot not ticked) and then install the OK1 baseband (auto reboot ticked, to allow reboot).