Android Lollipop is a version of the Android mobile operating system developed by Google , spanning versions between 5.0 and 5.1. Unveiled on June 25, 2014, during the Google I/O conference, it became available through official over-the-air (OTA) updates on November 12, 2014, for select devices that run distributions of Android serviced by Google (such as Nexus and Google Play edition devices). Its source code was made available on November 3, 2014. One of the most prominent changes in the Lollipop release is a redesigned user interface built around a design language referred to as " material design ". Other changes include improvements to the notifications, which can be accessed from the lockscreen and displayed within applications as top-of-the-screen banners. Google also made internal changes to the platform, with the Android Runtime (ART) officially replacing Dalvik for improved application performance, and with changes intended to improve and optimize battery usage, known internally as Project Volta. As of June 2015, statistics issued by Google indicate that 12.4% of all Android devices accessing Google Play run Lollipop.  Lollipop is succeeded by the Android M , which was unveiled in May 2015.