Update: Here's Andy Rubin's farewell letter to Android partners. (via The Verge)

Dear friends,

In November of 2007 we announced the Open Handset Alliance with 34 founding members. Today, I'm grateful to the over 85 OHA members who have helped us build Android and drive innovation at such an incredible pace. The Android ecosystem has seen tremendous growth since the launch of the very first Android device in October 2008. The volume and variety of Android devices exceeds even my most optimistic expectations - over 750 million compatible devices and counting!

At its core, Android has always been about openness - the idea that a thousand brains are better than one. Just as the ecosystem has grown, so has our team at Google. I am incredibly proud of the phenomenal group of people that spend their days (and nights) building the Android platform and services. Just look at last year...a lean yet incredibly ambitious team released Jellybean with Google Now, launched Google Play in many languages and countries and collaborated with several partners to build three new Nexus devices to help drive innovation in the ecosystem.

Today, the success of Android combined with the strength of our management team, gives me the confidence to step away from Android and hand over the reins. Going forward, Sundar Pichai will lead Android, in addition to his existing work with Chrome and Apps. Hiroshi Lockheimer - who many of you already know well - plus the rest of the Android leadership team will work closely with all of our partners to advance Android and prepare the platform for new products and services yet to be imagined.

As for me, I am an entrepreneur at heart and now is the right time for me to start a new chapter within Google. I am amazed by what we have accomplished from those early days (not so long ago!), and remain passionate about the power of a simple idea and a shared goal - an open source platform freely available to everyone - to transform computing for people everywhere.

Thank you for your support,

- andy

Breaking news from Google this morning - Andy Rubin is stepping down as head of the Android group at Google. He'll bee succeeded by current Chrome OS and Apps lead Sundar Pichai. Andy Rubin will apparently continue working at Google, just in a new - and as yet undefined - role. Here's Google CEO Larry Page's statement on the transition:

Sergey and I first heard about Android back in 2004, when Andy Rubin came to visit us at Google. He believed that aligning standards around an open-source operating system would drive innovation across the mobile industry. Most people thought he was nuts. But his insight immediately struck a chord because at the time it was extremely painful developing services for mobile devices. We had a closet full of more than 100 phones and were building our software pretty much device by device. It was nearly impossible for us to make truly great mobile experiences.

Fast forward to today. The pace of innovation has never been greater, and Android is the most used mobile operating system in the world: we have a global partnership of over 60 manufacturers; more than 750 million devices have been activated globally; and 25 billion apps have now been downloaded from Google Play. Pretty extraordinary progress for a decade’s work. Having exceeded even the crazy ambitious goals we dreamed of for Android—and with a really strong leadership team in place—Andy’s decided it’s time to hand over the reins and start a new chapter at Google. Andy, more moonshots please!

Going forward, Sundar Pichai will lead Android, in addition to his existing work with Chrome and Apps. Sundar has a talent for creating products that are technically excellent yet easy to use—and he loves a big bet. Take Chrome, for example. In 2008, people asked whether the world really needed another browser. Today Chrome has hundreds of millions of happy users and is growing fast thanks to its speed, simplicity and security. So while Andy’s a really hard act to follow, I know Sundar will do a tremendous job doubling down on Android as we work to push the ecosystem forward.

Today we’re living in a new computing environment. People are really excited about technology and spending a lot of money on devices. This is driving faster adoption than we have ever seen before. The Nexus program—developed in conjunction with our partners Asus, HTC, LG and Samsung—has become a beacon of innovation for the industry, and services such as Google Now have the potential to really improve your life. We’re getting closer to a world where technology takes care of the hard work—discovery, organization, communication—so that you can get on with what makes you happiest… living and loving. It’s an exciting time to be at Google.

Posted by Larry Page, CEO

Why step down now? It's hard to say - Larry's statement doesn't offer much insight. The fact is, Android has changed a lot since Andy came over from Danger Inc., and Google's mobile strategy has shifted from emphasizing an operating system to pushing products - devices, content, and services. We'd heard rumblings that Rubin wasn't exactly interested in that side of the business when the Play Store was spliced out of the Android group last year.

Pichai has been at Google since 2004, and previously lead the Chrome and Apps division. He was allegedly courted by Twitter back in 2011 to be the head of the company's product group, but stuck on at the big G. Pichai played a significant role at last year's I/O keynote with Chrome OS - an event Andy Rubin was absent from.