Update 8/18/18: It appears that Google made a server-side update last night which reverted the new Material Theme design with the dark theme.

Update 8/26/18: A new version of the app has rolled out which brings back both the Material Theme design and the dark mode!

Google has released the new Material Theme redesign for the Android Messages application in version 3.5.048 to all users. We discovered how to enable it way back in version 3.3 when it was first added as a hidden option, but now it's rolling out to all users. It's not just a completely rejigged UI, but the inclusion of a brand new dark mode as well.

The new UI itself is a complete re-write of the old one, and as such looks entirely different. Not only that, but there never was a dark theme for Android Messages either. This isn't the first Google-made application to be receiving a dark theme, as YouTube also has gotten one recently too. In countries where SMS is used heavily, the redesign of Android Messages will for sure be a welcome addition.

Google is redesigning a number of first-party applications to fit the new Material Design theme. This includes Google Photos, Gmail and more. With this release, it's possible that the floodgates may open to releasing even more material theme redesigned applications. It's an upgrade for sure and looks a whole lot nicer than the old design.

If you're wondering how to get the new update, you can download the latest APK from APKMirror below and install it. If you don't see the new design right away, force stop the application, clear the cache, and check it again. You may need to do this twice. It is definitely active in this version as many users on Reddit are reporting that they have the new redesign following an update from the Google Play Store. If it doesn't work, then you're probably just going to have to wait. It's unlikely to be a staged rollout as we did get it working on a OnePlus 6 not logged into a Google account. You can download the APK below.

Update: Google has reverted the change

It appears that Google has pushed a server-side update which disables the new design and dark theme. While dark mode wasn't mentioned in the changelog, the Material Design 2 redesign was. We'll be keeping an eye out to see if an official statement is released on why the changes were reverted.

Update 2: Android Messages new Material Theme design rolling out again

The redesign appears to be rolling back out again, according to many users on /r/GooglePixel. Here's the APK you'll need from APKMirror.

Android Messages with Material Design 2 and Dark Theme