Note that my title is a question. I am not sure if the image by Samsung US Twitter account is Samsung GALAXY S IV but since it mentioned the Unpacked event and #TheNextBigThing, I thought it might be referring to GALAXY S IV. Here is the image that I have enhanced.
Based on the outline, it sure looks like the leaked images. And the bezel seems smaller and the screen seems more to the top (means larger screen?)
Here is a comparison with Samsung GALAXY S III. Similar?
A few more days and everything will be clear 🙂