Sony Mobile has never officially confirmed that the Xperia SP is on the list to receive the future Android 4.4 KitKat upgrade. The only devices that will definitely get the update according to Sony are the Xperia Z, Xperia ZL, Xperia Tablet Z, Xperia Z Ultra and Xperia Z1 (we would imagine the Z1 Compact would also make the list).
However, Sony’s product pages for the Xperia SP did hint that Android KitKat is likely as far back as November 2013, with the version overview pointing to KitKat being a “future version”. This status has remained the same, until just now, when the product page has been changed to “Under Investigation”.
Given the delayed launch of Android 4.3 for Xperia SP owners, it was initially meant to launch by the end of 2013, maybe Sony has decided not to bother with KitKat. Or maybe, it still is on the agenda, but Sony doesn’t want to get people’s hopes up. Maybe it appeared on the “future version” as a mistake. At some point, Sony will clarify the upgrade cycle for some its lower-level handsets such as the Xperia L and Xperia M, so we hope to get clarity at that point.