I'll be the first to admit I didn't like ReCore, I did write a pretty scathing review of it after all. It seems things aren't looking much better post-launch as Destructoid has discovered that the fifth robot companion isn't actually in the game.
In ReCore you have four robot frames that you can find that'll give you various abilities and attacks. The game goes out of its way to make it look like there's a fifth frame as well. There's a slot for it, and hunting challenges for a fifth frame. The game's box art even shows a fifth robot in the background, clearly modeled after the tank enemies. There's even two sections of the map cut off by quicksand that you have no way to pass, all signs pointing towards the fifth robot taking care of that problem. Yet it appears there's no actual way to get this fifth robot at all, since it's just simply not in the game.
When Destructoid sent an e-mail to Microsoft the response they got was as follows:
The Tank is not currently available in the game. But please stay tuned for news.
While this does not say for sure, this does seem to imply that the fifth robot will be getting added to the game later. It's also not sure if, when it does get added later, it will be paid DLC or a free update.
This isn't the first time that ReCore has had a robot cut from it. The original announcement trailer shows protagonist Joule posing with six robots. The K-9, Ape, and Spider all made it into the game as is, and the Flyer is there albeit looking completely different than the final design. The Tank is there as well, seemingly having been planned from the start. Finally, there's a sixth robot that appears to be a flying sphere of some kind. It's unknown when that one was cut, if it'll be added back to the game, or what its original purpose was.