Update 27.08.2016: It also works for version 23.5.A.1.291 (OS update that includes STAMINA). The procedure is identical, you just have to use the latest firmware available and create a pre-rooted .zip to update your tablet device.
I am pretty sure that I couldn't find a how-to guide anywhere that explains how rooting our precious Xperia Z3 Tablet Compact on Android 6.0.1 with locked bootloader works. This post simply shows the process of how I got root on my device (SGP611) and I am going to write the steps only in moderate detail so that hopefully everyone can follow without hassle. There are some steps that I'm not going to explain too much in detail but instead I highly recommend you to look around a bit on XDA to find theses already explained steps (I just want to get to the point on how to get root so that's why it may not be super noob friendly).
Edit: A little bit more info and additional steps that might help you further can be read in post #5.
Your warranty is now void.
I am not responsible for bricked devices, dead SD cards, or any other issues that may arise from not following the steps correctly/carefully.
1. Downgrade device if necessary
2. Root using KingRoot exploit
3. Install XZDualRecovery custom recovery
4.1 Get the latest Marshmallow firmware and create FTF file
4.2 Create the pre-rooted .zip file
5. Flashing the pre-rooted .zip file correctly
Extra: Already created pre-rooted .zip file download for the lazy ones (At the very bottom)
1. First thing you need to know is that if you're device is currently bootloader locked and on Android Marshmallow 6.0.1 (23.5.A.0.575), as of the time I am writing this, you will not be able to achieve root directly through some kind of rooting tool. What you need to do now is to downgrade your device to an older version of Android, e.g. Android 5.0.2 or KitKat are good enough.
To do this you need to find the older firmware:
-Try this link to look for it: http://xperiafirmware.com/ (If you can't find Android 5.0.2 for example, use Google or look around XDA)
-Downgrading the device will wipe data/factory reset, so BACK UP YOUR STUFF before downgrading.
-Use flashtool to flash the firmware and downgrade: http://www.flashtool.net/index.php (I will expect you to know how to use flsahtool to flash ftf. files, there are many tutorials on how to do this)
2. Why you have to downgrade is because older firmwares have an exploit that can be used to root the device even when the bootloader is locked. So yes, something like a one-click root method is possible now.
-You may use this tool called KingRoot to root your tablet: http://forum.xda-developers.com/andr...x-5-0-t3107461
Read the info carefully before doing anything.
3. Now, you should have managed to root your device with Android version other than 6.0.1. That is when another great tool comes in which is called XZDualrecovery. XZDualRecovery is "a" custom recovery that you'll need to be able to proceed from here.
-Install XZDualRecovery using the root method. That's the only way to get it onto the device.
-Link: http://forum.xda-developers.com/show....php?t=2261606 (Read the instruction there carefully)
4. Great! Now you should have root and custom recovery. If not, you did something wrong.
This is when you can create something called a "pre-rooted" firmware which is basically all you need to get root on Marshmallow 6.0.1.
-Use the tool called Xperifirm to download the Android 6.0.1: http://forum.xda-developers.com/cros...oader-t2834142
-Launch Xperifirm and on the left hand side browse to "Xperia Z3 Tablet Compact -> the model number of your device (look under settings on your device to find out model number)"
-On the right side top you'll see "Check all", click it to let it check for latest firmware number
-Android 6.0.1 would be
-After downloading you'll need flashtool again to convert those downloaded files to .ftf format (Again, there are instrutions on the internet that you can look for)
-Make sure you have the .ftf file
-Get two .zip files
--1) RecRoot: http://forum.xda-developers.com/z3/g...-0-mm-t3337357
--2) A dummy flashable file: http://forum.xda-developers.com/z3/g...9#post66569699
-Get PRFCreator: http://forum.xda-developers.com/cros...e-pre-t2859904
-Open PRFCreator and put the .ftf file to FTF, the RecRoot .zip file to RECOVERY, and the dummy_flashable.zip to SUPERSU. Don't do any other way!
-Tick Kernel, FOTAKernel, Modem, LTALable and Sign Zip
-Click "Create" to create the pre-rooted Marshmallow firmware
5. You should have created the pre-rooted Android 6.0.1 firmware now.
-Put the pre-rooted .zip file and the RecRoot .zip file onto your device's SD card/storage (anywhere where you can find them later)
-Reboot your tablet into TWRP recovery. (XZDualRecovery even provides you an app to choose and reboot to recovery) Don't reboot into any other recovery!
-Now, in TWRP recovery, erase dalvik cache, cache and system just to be clean.
-FIRSTLY, flash the pre-rooted.zip that you have put on your device. After flashing successfully, DON'T REBOOT YET!
-SECONDLY, flash the RecRoot.zip file
-Now you can reboot and if you did everything correctly, your Z3 Tablet Compact should boot up with Chainfire's SuperSU root and TWRP recovery (to access TWRP recovery, you have to reboot the device and while a green LED light appears for a moment, press and hold the volume down button. Then you will enter TWRP recovery. As for now, you cannot access the recovery any other way like using a reboot app, it will not work!).
CONGRATULATIONS! You have a rooted Z3 tablet with locked bootloader and you haven't lost Sony features.
Thank you for reading this tutorial. And don't forget to thank all these devs that provided us the needed tools.
Extra: I will also put a link here where you can download my created pre-rooted Marshmallow firmware. It's build 23.5.A.0.575 Customized Germany and for SGP611 only!