Cross-posting with Instagram used to be a one-way street. Instagram users were able to share their Stories to Facebook, but not the other way around. Now, the company is working on a new tool for Facebook Stories users to cross-post to Instagram Stories. App researcher Jane Manchun Wong first discovered the "Share Story to Instagram" toggle within the Story Privacy settings. If you switch this feature on, a "Share to Story" button will appear on your post.
Facebook confirmed that it is testing the feature now. It isn't clear when it will be widely released or if it will allow both apps to sync a Story's view so you can avoid watching the same cross-posted Story twice. But we will let you know for any updates.
Source: Engadget