It looks like one of Square Enix' unannounced titles for Electronic Entertainment Expo (E3) 2018 has been leaked ahead of time. One user noticed that a Steam news item for Just Cause 4 and sent out the call to the internet.
We here at USgamer independently opened Steam to confirm that yes, this is a real image that greets everyone when they load up the client.
Square Enix will once again be handling publishing duties for Just Cause 4. The previous Just Cause games were developed by Avalanche Software; if they are developing Just Cause 4, this would make three titles the studio is working on, including Rage 2 and the newly-announced Generation Zero.
The Steam news item doesn't lead to an actual store page yet, so this looks like a case of bad scheduling. We'll have more on Just Cause 4 as we roll into E3 next week.