Multiple references to something called XCOM: Enemy Within have surfaced, and while 2K has no news to share right now, we don't have long to wait.
The listings, which seem to have been first spotted by CVG, give no clue as to what the title may refer to.
A request for comment from 2K yielded the following statement:
"We’re looking forward to making an announcement on August 21. We don’t have any further comment at this time."
Speculatively, we could be looking at an expansion or DLC for XCOM: Enemy Unknown.