How to install the Google Keyboard 4.0 from Android Lollipop on your device right now
1. Just download the Google Keyboard 4.0 APK file, and install it on your handset;
2. Go to the language and input settings menu, and enable the Google keyboard as default. If you want to change the theme, go to the keyboard's settings, and choose one of the four available, which include the two Lollipop ones.
That's all folks, now you have the pretty new Material Design Google keyboard on your handset without breaking a sweat, in all its Light and Dark themes glory.
source: Shaftamle (XDA-Devs) images: AndroidPolice
Things that are NOT allowed: