The Callisto Protocol is no longer set in the PUBG universe and now takes place in its own world with its own independent story.
Although reactions to The Callisto Protocol so far have mostly focused on how scary the aliens look and how much it resembles Dead Space, one of the most interesting things about the game is that it was originally announced to take place in the PUBG Universe, albeit hundreds of years in the future and on a completely different planet.
The insistence that The Callisto Protocol takes place in the PUBG universe despite the massive time and location difference was one of the more intriguing parts of the game, but it looks like that's since been changed around. Creative director Glenn Schofield Tweeted about the game's relation to PUBG following a recent blowout of information for the game, revealing that it was now its own thing entirely.
Schofield said, "FYI The Callisto Protocol is its own story and world. It no longer takes place in the PUBG Universe. It was originally part of the PUBG timeline, but grew into its own world. PUBG is awesome, & we will still have little surprises for fans, but (The Callisto Protocol) is its own world, story and universe."
It seems that The Callisto Protocol's connection with PUBG has always been pretty slim, as Schofield said as much in interviews closer to the game's reveal. Here's what he previously said to Game Informer about the connection to PUBG, "When we came in, they had a lore team and they were writing this big story, like, ‘Where does PUBG start? Where does it fit in?’ They write this giant timeline and our writers are involved in helping. We sit on the timeline, but we sit pretty far out there, and kind of alone. So if they ever make another game, let’s say that’s after our timeline. I would imagine our game will inform that more than we are being informed by their timeline.”