By pre-order now you can in fact infiltrate with early alpha access. The core mechanic of turn-based sneakery is in, but major content is "still being implemented."
"We expect the game to change significantly as we test and release new updates, and as much as we try to keep them out, we’re expecting bugs along the way," said Klei.
Currently early alpha access is available only for the PC platform. Theis running a discount for the game with 15% off the standard game at $16.99, or 20% for the game and soundtrack at $19.99. Incognita is due to fully release sometime in 2014.