Xperia Overlay is custom firmware designed for the 2011 Sony Xperia HDPI devices such as the Xperia Arc, Arc S, Neo, Neo V, Pro and Xperia Ray. The firmware has been developed with Sony’s Firmware Overlay source code rewritten by the Xperia Overlay Dev Team (including members Achotjan and MarioJerkovic from XDA) and merged with AOSP.
Xperia Overlay is using the Xperia Z2’s Android 4.4.2 firmware, bringing it to 2011 Xperia HDPI devices. If you want to try this firmware, you will need to have an unlocked bootloader and download the necessary files from XDA, you can then install using CWM Recovery.
Thanks to all that sent this in!