Screenshots show players with Hunter Rank 999 in Monster Hunter: World. However, their legitimacy is questionable.
The Hunter Rank in Monster Hunter games can be compared to character levels in RPGs.

Depending on how high or low your rank is, you have access to certain quests, weapons, and equipment.
Real or Fake?
For a long time, it was unclear whether MHW has a cap for the Hunter Rank and if so, how high it goes.

Now it seems that various screenshots prove that the first players have managed to reach the maximum Hunter Rank in MHW.
The problem, however, is that such screenshots first appeared on February 15, shortly after the game’s release.
MHW HRカンスト! #MHW #PS4share pic.twitter.com/ijBymADKvi
— fixates (@fixa3rd) February 15, 2018
Since the save files for MHW are stored locally and can be easily edited, most of them are most likely fakes.

But even if these screenshots were created by manipulating the save files, one could still assume that this is the actual maximum Hunter Rank. In previous Monster Hunter games, the cap was at 999, so a maximum Hunter Rank of 999 in MHW would make sense.
You can learn more about the Hunter Rank in our article:
What is the Hunter Rank in Monster Hunter World and how do you level it up?