Android OS 4.4 KitKat has slowly increased its ranking over the past 4-weeks by 0.03% to 1.4% of devices (might be a slight insight into how Nexus 5 sales are doing, too). The main player is Jelly Bean with an adoption rate of 59.1%, up 4.6% from last month. OS 4.0 Ice Cream Sandwich still claims ownership on 16.9% of all Android devices. Unfortunately, those on Gingerbread — which was officially released December 2010 — are still a substantial number with 21.2% of Android users.
Source: Android Developers