On Word Flow's Microsoft Garage page, the company notes that "the Word Flow experiment is now complete," and suggests that users download SwiftKey. Microsoft acquired SwiftKey in February of 2016, so it appears that the company has decided to focus solely on one predictive keyboard app on the iOS App Store.
As with all apps removed from Apple's App Store, when attempting to visit old links for Word Flow on iTunes [Direct Link], an error message now reads, "The item you've requested is not currently available in the U.S. store."
The Word Flow experiment is now complete! We encourage you to download the SwiftKey Keyboard from the App Store. The SwiftKey product team is frequently building and evaluating new features for SwiftKey and shipping updates.Like many third-party keyboard apps, Word Flow incorporated GIFs, theme customization options, and machine learning for better predictive texts. The app's standout feature was "Arc Mode," which curved the iOS keyboard into a circular shape and hugged the side of the iPhone that a user would type on, allowing for comfortable one-handed typing.
Now that it's gone, users won't have access to Arc Mode, but SwiftKey includes many of the same features as Word Flow, including a swipe-to-type ability. The app was updated about two weeks ago with emoji prediction, new themes, upgraded 3D Touch features, and more languages. SwiftKey is available to download from the iOS App Store for free. [Direct Link]