According to sources familiar with the situation, 9to5Mac is saying that Facebook is "preparing major update" to a bunch of the apps in its purview. This includes the basic Facebook for iOS, the Facebook Messenger app, and Instagram.
First off, prepare for Graph Search on your Facebook for iOS app.
A couple of months ago, Facebook pushed Graph Search to everyone in the U.S. When making that announcement, the company reiterated that they were working on adding more functionality to it (the ability to search statuses, comments, etc) and that they were working on bringing it to mobile. Well, they've already done the former, and it appears that the latter is coming soon. We knew that Graph Search would eventually hit mobile, and 9to5Mac says that an impending app update will incorporate it into the main search bar on the app.
As far as the coming changes to Facebook Messenger...
In addition to the aforementioned update to the main Facebook for iOS application, Facebook is preparing a redesign of its Messenger app. Facebook is said to be internally testing two new versions of Messenger. The first version is said to look largely similar to the Messages application bundled into iOS. That version includes green interface elements. The second version in testing, which the source says is more likely to ship to end-users, is heavy on white space and very fitting for iOS 7′s design. It is not filled with blue interface elements like the new Facebook app. The new app has tabs for active/recent chats, contacts, and settings across the bottom…
Oh, and the team is also working on bringing some more video filters to Instagram.
Lately, Facebook's been on a pretty strict app release update - pushing something new about once a month. Hopefully this means that we'll see the aforementioned changes in an update before October's over.