This will be done through an episodic release, meaning that every couple of weeks/months, new content for the game will be released. In fact according to the game’s executive producer Hannes Seifert, he told the folks at GameSpot that Day One content for the game is expected to be announced soon.
This is basically the content that gamers can look forward to on the first day. According to Seifert, “We will be extremely precise with that within a few weeks after Gamescom. We know that our players need to understand what they’ll get for their money.” The studio is also taking an interesting approach in which they will not charge for DLCs.
Some games come with a Season Pass which is basically pre-purchasing the DLCs ahead of time, but with HITMAN there will be no in-game purchases, what you pay for is what you will get and for years ahead. In fact Seifert expects that the new HITMAN game to last a good 3-4 years with new content being churned out on a constant basis.