In Android 4.4 KitKat, Google introduced a new optional runtime simply called Android Runtime. It will one day replace the current Dalvik and for good reason, it’s faster, more efficient, and breathes life into older devices like the Galaxy Nexus. Switching to ART isn’t as obvious as some might like, so simply follow the steps below to switch.
1. Go into settings. You can do this by accessing the quick settings menu in the notification bar.
2. Go into Developer Options. If you don’t see developer options you might not have them unlocked yet. You can unlock developer settings by tapping on the Build Number in the About Phone section several times.
3. Select Runtime. Once you are in Developer Options you can immediately see the “Select Runtime” option. Click that and select “Use ART”. Your phone will reboot and spend a few minutes optimizing your apps for ART.
Keep in mind that ART isn’t available for all devices officially. Some devices like the 2012 Nexus 7 don’t have access to ART in the stock ROM. On most devices this works with custom ROMs such as CyanogenMod 11.