Here is a Thief 4 video showing some artwork from the game, which is still a long ways off.
These comments come from the head honcho of Eidos Montreal Stephane D’Astous who stated that Deus Ex: Human Revolution was such a success for the developer (and likewise for publisher Square Enix), that they now have more clout and the credibility to aim higher and be trusted to deliver. It also brought the developer more confidence and means they can cut through the “red tape” of game development quicker thanks to having a hit title and sales behemoth like Deus Ex: Human Revolution under their belt.
However they also warn that, due to that success of Deus Ex: Human Revolution, they now must hit it out of the park even above and beyond with Theif 4, and make sure that the game is BETTER than Deux Ex: Human Revolution, while ensuring that it is just as much a hit if not more so, or else the developer may be labeled a “one-trick pony”.
Thief 4 will include various open-ended options that players can choose that changes how they play, just as you’d expect and in keeping with most games these days that allow players to play the game exactly how they want with varied gameplay.
The game will also run on the Unreal Engine. Although its very far off, and probably won’t hit until Winter 2013 at the earliest.