The latest version of Android is on the rise. Last month, Android 4.4 KitKat sat around 2.5% and that number has doubled since to 5.3%! As more flagship devices running KitKat have yet to be released, May and June will likely see rather large increases. Also, some older devices are going to be getting KitKat as well. Its predecessor, Jelly Bean, saw just a minor drop in percentage points.
Thankfully, older versions of Android are seeing declines. Gingerbread dropped 1.2% and somehow Honeycomb is clinging on for dear life. At some point this year, I do expect Honeycomb to let go. A version like Ice Cream Sandwich can stick around a little bit longer since its core does resemble more recent versions; however, updates to Jelly Bean are still expected.
Source: Android Developers