Kojima Productions contacted the insider Tom Henderson via email asking him to remove the article on Overdose, his supposed next game. Henderson reported the matter on Twitter, stating however that he did not comply with the request, as verifiable by the fact that the article is still online.
For many it was enough to confirm the goodness of the leak, that is, the existence of Overdose. On the other hand, if not, why would he have asked for the article to be deleted? So we can expect Overdose to be unveiled to the public in the next few days. It is not yet clear whether at the Summer Game Fest or on another occasion, even if a tweet from Geoff Keighley points more towards the first hypothesis (moreover he and Kojima are great friends).
Of course, nothing is confirmed yet, but in this case we are far beyond mere suspicion. Overdose could therefore actually be the horror of Kojima Productions that has been rumored for a long time in the past few years, practically since the launch of Death Stranding.
For now, the game is known only as reported by Henderson, namely that it is a horror in the third person, playable even in the first. We will certainly know more when it is shown.