The Galaxy S6 and S6 edge is not the latest Samsung smartphone, but these devices are still supported to get the latest version of the Android OS. In the US, several variants have been upgraded to Android 6.0 some time ago, like the Sprint and the Verizon. And now, the T-Mobile variants (SM-G920T and SM-G925T) also updated to Marshmallow. For advanced users who like to mods its device, there is nothing to worry about it, since root on Marshmallow for T-Mobile Galaxy S6 and S6 edge is still achievable.
The update was released via OTA so that you can instantly download and install the update directly on the device. It’s released with G920TUVU3EPD1 and G925TUVU3EPD1 software version, both have the same software version, possibly that is why the OTA updates are released at the same time. Based official T-Mobile support site, there’s no additional features or functionalities, so it just brings the Android 6.0.1 primary benefits like Now on Tap, Doze and enhanced app permissions.
If you have been rooted, currently running a custom recovery (TWRP) and would like to install the update via OTA, we encourage you to restore the phone back to stock, since the update file can only be installed if the device runs untouched systems or in stock condition. You also have an option to manually install the update via the Odin flash tool, it’s required an Odin compatible firmware.
For those who need superuser privileges, you can regain root on Marshmallow for T-Mobile Galaxy S6 and S6 edge without difficulty. Simply because the phone comes with an unlockable bootloader that could open any possibilities to mods this device. Some xda members have successfully rooted once they get updated to G920T/G925TUVU3EPD1 software version.
However, there is little difference of the method to root Android 6.0.1 in both devices:
Galaxy S6 (SM-G920T)
For this device, you can try to flash the TWRP by idlekernel with Odin tool, then flash SuperSU package (tested with SuperSU v2.71) with the installed TWRP, and do not forget to turn on the Enable OEM Unlock in Developer options. But there are some folks who also try to add a custom kernel by HackerKernel (v14), but it triggers incall audio problems.
Galaxy S6 edge (SM-G925T)
There is no significant difference to the edge models, after successfully updated to Marshmallow, you will need to flash the TWRP recovery by arters via Odin flash tool. Then after it successfully installed, use it to flash SuperSU zip (tested with v2.71). The result may vary, there are some members who have audio and Wi-Fi calling issues just after rooted.