There are currently 4 allies, with 2 more on the way. There's still quite a lot of content (allies, weapons, perks, crafting options, dialogue encounters, maps) to come!
To explain a little more on the number of allies. While it would have been possible to add more, it would have come at a cost in how well defined they are: things like voiceovers, unique perks, interacting with allies in dialogue, etc. So with the option of having a larger number of less defined allies, or a smaller number of better defined ones, and a max team size of 4, the latter seemed like a better idea.
