Last week Google announced a revamped Gmail experience across both its Web and mobile services. The Web version rolled out later on that same day. We already covered, and how to use it once you do, but Android version 4.5 was said to begin rolling out in the coming weeks.
Thanks to Android Police, who happened to grab the Gmail APK, you can download and install the revamped version of Gmail for your Android device right now.
You'll need to download the APK from one of the mirrors on the Android Police post, and then sideload it onto your device. Make sure you allow apps from unknown sources to be installed, which is usually in the Settings under Security, before trying to install the app.
Your phone will need to be running Android 4.0 and above to take advantage of the new features.
If sideloading the app isn't something you want to do, you can wait for the update to become available on your device. You'll need to keep checking the Play store to see if it's available for you.