In the announcement post, McMillen focused solely on the Xbox One version and said that “it will obviously not release with the upcoming afterbirth dlc, because it isnt finished yet, but it will eventually make its way to the ol bone.”
Alongside this release date announcement, McMillen also revealed a couple more details about what will be contained inside the Afterbirth DLC. The first is a golden question mark box that adds the symbol to Isaac’s forehead. When it has been collected, the treasure rooms that you find in the game will become double treasure rooms – in other words, there will be two items inside them instead of one. And yep, double treasure rooms is the other reveal. Without this new item there’s only a tiny chance of double treasure rooms showing up but with it you should come across quite a few.