KitKat and Lollipop still comprise the bulk of Android installations.
Google has released the latest numbers for the various versions of Android running on our devices. For the week ending June 6, 2016, some 10.1 percent of all current devices that utilize Google's services (that excludes Android devices in, say, China, as well as Amazon's derivatives) were running on Marshmallow, up from 7.5 percent the month before.
Android 5.x Lollipop remained about the same at 35 percent of installations. The aging Android 4.4 KitKit fell about 1 percentage point, to 31.6 percent. Android Jelly Bean — which spanned Android 4.1.x to Android 4.3 — fell slightly from 20.1 percent to 18.9 percent. The legacy versions — Froyo (Android 2.2), Gingerbread (Android 2.3) and Ice Cream Sandwich (Android 4.0) — made up just 4.3 percent of all devices currently pinging Google.
In September 2015, Google announced that more than 1.5 billion Android devices were active worldwide. That number has almost certainly grown since then.
Android platform versions over time
For context, we're charting the progress of the various versions of Android as they move through their lifespan. The most current numbers are to the right of this chart. The more broad a swatch of color, the higher the percentage. A version will start at the lower right of the chart and trend to the left over time, before finally tapering off at the top of the chart as it moves left.
Inside the versions of Android
What's the difference between Gingerbread and Jelly Bean? How is Lollipop not like KitKit?
Android moves quickly. It can be tough to keep up with all the changes. (It's tough for us, and we do this for a living!) So we've got a primer on all of the different versions of Android, from Cupcake to the current builds. It's the tl;dr you need to keep all the versions straight.