Google introduced Android L at I/O 2014. Android L has a new look and to keyboard thanks to the "Material" design. Android L keyboard has gone flatter and has new animations in it. The Android L Keyboard is now available in Google Play . The app installs just like any other third-party keyboard app – no root required, no side- loading and no need to remove Google Keyboard etc. You install Android L Apps, Bootanimation, Ringtones, Wallpapers on any Android device.
Download: Android L Keyboard from Google Play Store
Or you can try the apk installation method by XDA member "asdfzz"
How to Install Android L Keyboard via APK (For Rooted and Non Rooted)
1. Uninstall Google keyboard (Play Store one not AOSP) if downloaded from playstore.
2. Download the Android L Keyboard apk from here
3. Install the apk and change theme. Go to Android L Google Keyboard settings > Open “Advanced settings” > Select Color scheme “Material”