The official Facebook app for Windows Phone is developed by Microsoft, and is always behind when it comes to new features released by Facebook for their iOS and Android app.
It seems Microsoft has decided they have had enough of this, and will be accelerating the development of the app.
They have released a private beta of the app, version 5, into marketplace, and are looking for active beta testers to volunteer to test the app.
The new app included new support for high-res photos, post sharing, and Facebook Timeline, and Microsoft hopes to generate a lot of feedback via the app itself (under Settings> About) and even via the review section of marketplace.
If you are the adventurous type you can grab the beta app here. The beta is WP8 only.
Via the Windows Blog.