Andy Rubin no longer leading Android, replaced by Chrome exec Sundar Pichai (update: memo)

There's a big upheaval afoot at Google -- Android lead Andy Rubin is stepping down from his position to "start a new chapter" at the company. Sundar Pichai, who currently oversees the Apps and Chrome projects, will take over the top spot in mobile. Neither the company nor Rubin have explained the reasoning for the management change so far, although it's safe to say that Rubin is going out on a high note when most smartphones sold today use the OS he helped create. CEO Larry Page mentions 750 million Android device activations as of Rubin's move, and over 25 billion cumulative Google Play app downloads.

Update: The Wall Street Journal has posted a memo from Rubin to partners. If you're looking for deep insight into why he's stepping down from his definitive role, you won't find it: Andy mostly reiterates that he's staying with Google and is an "entrepreneur at heart," which suggests that the change may be spurred more by personal interest than corporate maneuvering.