It is certain that Sony will not release Android Marshmallow update for Xperia M, as it is a too old device to get manufacture’s support. Therefore, Xperia M owners who are excited to get the new Android 6.0.1 Marshmallow, try the official CyanogenMod 13 (Nightlies) ROM. Checkout the following installation guide to know the prerequisites for flashing the ROM and download links.

To install CM13, your Xperia M (C1904, C1905) should be running on the Android 4.3 Jelly Bean, have unlocked bootloader with root access and latest version of custom recovery installed (CWM or TWRP). This official Nightly will not support Xperia M Dual model. Note that, the ROM status is nightly, which means unstable. However, the update is reasonably stable with most features working.

How to Install CyanogenMod 13 (Android 6.0.1) on Sony Xperia M

Prerequisites: a) Xperia M should be running on Android 4.3 Jelly Bean b) Unlocked bootloader and rooted with latest version of TWRP custom recovery installed. c) Backup every data on your phone. Also, make system dumb (Nandroid backup) in TWRP recovery, just in case anything goes wrong. d) Your Sony Xperia M charged up to 80% to avoid shutdown during the flashing process. Installation Instruction:

  1. Download CM13 ROM zip file (nicki) [HERE] and Android 6.0 compatible GApps package [HERE]. Transfer the downloaded zip files in your SD card
  2. Boot your phone into TWRP recovery. To do so, switch off your device, press and hold Vol Up + Power button simultaneously.
  3. In recovery, backup stock ROM by taping ‘Backup’ option, if you have not already done.
  4. Once done, tap on ‘Wipe’ and select cache, system, data and dalvik cache. Swipe to confirm wiping.
  5. Now, tap on ‘Install’, select CM13 ROM zip file and then Gaps zip file and swipe right to confirm flashing.
  6. Once the installation process is completed, reboot your device. Your Xperia M will boot into Android 6.0.1 (CM13) after a few minutes. Sep up your account and enjoy. Troubleshooting
  7. If your phone gets into the boot loop sequence (stuck in the welcome screen), boot your phone into custom recovery, wipe cache and dalvik cache.
  8. If above procedure is not helped you, follow the above installation instructions again.