On KitKat, ART can be enabled from an Android device's hidden developer options, but the developer homepage explains that "Dalvik must remain the default runtime or you risk breaking your Android implementations and third-party applications," and adds that "some techniques that work on Dalvik do not work on ART."
The only downside of ART at the moment is that apps take up more storage space and install times are also longer. However, Google might improve the current performance by the time it releases the next version.
First spotted by XDA Developers, the code commits made to AOSP's master branch feature a statement - "Dalvik is dead, long live Dalvik! DO NOT MERGE".
This is by far not an indication that Android devices running KitKat will immediately start using ART as a default, or that code changes will be made by Google in the next minor iteration of Android. Notably, Google just released an incremental update to Android with security fixes, bringing the version number up to Android 4.4.4.
The update might be featured in the much-anticipated Android 5.0 version that Google is expected to launch at I/O 2014 next week.
We had recently reported how Android 4.4.x KitKat was present on 13.6 percent of all devices running Android. On the other hand, the Android Developers website reported that Android 4.3 Jelly Bean was installed on 10.3 percent of Android devices.