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AOSP stands for Android Open Source Project. In a way you can tell it is Stock Android source code, from which whole firmware can be built and then it can be used as Stock Android ROM.Many ROMS you will find are also AOSP based, one of the most common example is CYANOGENMOD and you can find several other independent too.
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Though I hope Sony does release Android Kitkat for Xperia L, this AOSP release means that Sony has tried testing Android 4.4 on Xperia L but I cannot say clearly that it will be released.
I would like to tell you that this is not an update. It is just that Sony has released source code for Xperia . Its meant only for developers to build ROMs, kernels etc. And all other developer stuff. It will require you to Unlock your Bootloader. You cannot download directly from the site. You will need to know how to work with Linux and then you will have to download the source through Linux. And then you will need to build it yourself. I don't think (no offense but) you know how to do that. Even I don't have Linux.
But there is a way you can go to XDA forums and download the ready made ROM built by a developer.
If you want to do so I will provide link.
http://forum.xda-developers.com/xperia-l#romList
on this page you will find all ROMS including 4.4 based ones.
Sony Released the Open Source Archive for the Xperia L's upcoming Firmware build 15.3.A.1.12.Sony uploaded the file yesterday so we might get the update today or within a week. Still no info about the Android version. it's likely to be a Android 4.2.2
Sony Released the Open Source Archive for the Xperia L's upcoming Firmware build 15.3.A.1.12. Usually Sony release open source archive for a build after the particular build is released so this might hint us the new firmware will release very soon. Sony uploaded the file yesterday so we might get the update today or within a week. reports says Xperia L's CM11 developer Brinly Taylor has already examined the package and found that the display driver has been updated along with increase in display frame rate. we believe, that will fix the screen flickering and multi-touch issues. Still no info about the Android version. it's likely to be a Android 4.2.2 , If you are a developer or a expert in this field download the package from this link and do tell us more info you found.http://developer.sonymobile.com/downloads/xperia-open-source-archives/open-source-archive-for-build-...
So will there come a day when sony will give us Android 4.4.2 update??
Xperia M got the 4.3 update. Why is sony neglecting Xperia L 