Other improvements include performance tweaks and one-tap photos.
Here are more details on the updated app, from the Windows Phone Blog:
An update to Messenger for Windows Phone is rolling out today, bringing performance improvements and new features. You will see better performance in a few areas. In the background, Messenger is doing more caching of images (like stickers) for better data consumption. Taking and sharing a photo is much quicker: You can take and send a photo with just one tap. You don’t have to leave the app to take a photo with a separate camera app. There is a brand new photo gallery feature built into Messenger that gives you quick access to photos on your phone without leaving the app!
You will also see a new groups tab where you can manage and create groups with your closest friends, family, or work colleagues and have group conversations. You can pin these groups to your Start screen, as well, for quick access.
Windows Phone users: Have you updated your apps yet? What do you think of the changes and additions?