Sony has made the decision to pull the plug on three of its phones - the Xperia M (and M Dual), Xperia L and Xperia SP will not be updated anymore, leaving them at the current latest software version.
For the Xperia M, Xperia M Dual and Xperia L that's Android 4.3 Jelly Bean, which was released in the first quarter of this year.
The Sony Xperia L will be left a step behind that, Android 4.2 Jelly Bean, which was released in October last year.
All three Xperia models have a gig of RAM and two Krait cores so they should be able to run KitKat quite fine. For that you'll have to go the unofficial route though, CyanogenMod has nightlies for CM11 for them.
If you're curious about the state of the software of your Xperia smartphone, you can check the Xperia care...