SAN FRANCISCO—We're live from Google I/O 2014, where Google has just taken the wraps off the next version of Android, dubbed the "L release." The new OS is Google's follow up to KitKat, which came out last October.

"It has over 5,000 new APIs," Google's Sundar Pichai said, adding that the OS is "designed for form factors beyond mobile." The L developer SDK will be downloadable on Thursday, June 26, directly from Google, while the full public release is expected "this fall."

Android Design Lead Matias Duarte took the Google I/O stage to describe L's big UI changes, particularly Polymer, which offers new typography, grid structure, and colors by default. L brings prominent new animations throughout Android, most noticeably a "ripple" effect in messaging, phone dialers, and more. (The Android font "Roboto" sees a tiny tweak as well.)

David Burke, director of engineering at Android, followed up to describe animation changes in L, particularly "seamless animation transitions" between apps. "We wanted to give you early access so you could bring Material to your apps," Burke said to developers, as he demonstrated changes like "enhanced notifications" and "analyzed user behavior" in a lock screen.

Demonstrations of Web browsing showed off a wealth of new animations, along with individual Chrome browsing tabs becoming part of a user's total "recent apps" log, while a demonstrator addressed touch latency, assuring developers that they'll receive a few more frames of notice so that apps can react to touch more quickly.

Third-party developers applauded when they learned that all apps can now connect to Google search results, where L will open relevant apps—demoed with OpenTable at I/O today. This option was limited to very few apps up until this release of Android.

A battery-minded initiative called Project Volta also saw an announcement, complete with the stat-loaded Battery Historia and a Job Scheduler API that will allow apps to react to battery conditions like being plugged in or running low.

Modern ART

As was long indicated by Android Open Source Project commits, the L release replaces Android's runtime, Dalvik, with ART, the Android RunTime, offering "twice the performance improvement" to all apps.

The runtime is the engine that Android apps run on. When you hear about Android apps running on BlackBerry 10 or Windows, those solutions are implementing Dalvik. While Android has changed significantly over the years, Dalvik was one of its oldest components. It was originally designed to save space (PDF), not to be fast or battery efficient. With ART, Google is ripping out one of the oldest core Android components and replacing it with a speedier, more modern implementation.

This isn't the first time we've seen ART. A beta version of it shipped as an option in KitKat, which allowed app developers to make sure the new runtime didn't cause problems with their apps. In L, Google has dumped Dalvik and made ART the default runtime.

Dalvik used JIT, or just-in-time compilation, meaning that an app was compiled every time it was run. ART switches to Ahead of Time (AOT) compilation, meaning that the app is compiled once. Traditionally, JIT takes longer to start up but can be more aggressively optimized because it has information about the device it is running on. AOT will start up faster, but it usually has less information about the hardware it's running on.

With ART, Google ships uncompiled code through the Play Store and compiles it at install time. ART uses AOT compiling, but it is compiled on the device, meaning it has much of the information JIT has about the hardware it is running on. This, combined with a modern, complete overhaul with a focus on speed, means that ART should be a lot faster than Dalvik. The only downside is longer install times and maybe a few incompatible apps from developers who didn't take advantage of the KitKat preview. We'll be sure to give L the full benchmark treatment as part of our review.

Technology reporter Sam Machkovech contributed to this report.