As of November 2013, current Android versions consist of a kernel based on the Linux kernel version 3.4.10, while Android versions older than 4.0 Ice Cream Sandwich were based on the Linux kernel 2.6.x.
Android’s Linux kernel has further architecture changes by Google outside the typical Linux kernel development cycle. Certain features that Google contributed back to the Linux kernel, notably a power management feature called “wakelocks”, were rejected by mainline kernel developers partly because they felt that Google did not show any intent to maintain its own code. Google announced in April 2010 that they would hire two employees to work with the Linux kernel community, but Greg Kroah-Hartman, the current Linux kernel maintainer for the stable branch, said in December 2010 that he was concerned that Google was no longer trying to get their code changes included in mainstream Linux. Some Google Android developers hinted that “the Android team was getting fed up with the process,” because they were a small team and had more urgent work to do on Android.