Alleged Grand Theft Auto 6 leaks are so plentiful you could fill a stadium with them, but occasionally some stand out from the crowd by either being more plausible or ridiculously bold faced.
You can decide for yourself which category you think this latest, massive GTA 6 leak belongs to.
4Chan is pretty notorious as far as websites go, and is known for being a haven of video game leakers — among a laundry list of other, unsavory stuff that isn't allowed anywhere else online. While most game related 4Chan leaks end up being duds, there is a reasonably high margin of info that turns out to be legit.

Recently someone claiming to be a "primary developer" at Rockstar Games held a pair of AMA — "ask me anything" — sessions on the site. The leaker remained anonymous, allegedly to protect their career, which greatly damages the credibility of the information posted. Moderators swiftly removed the first AMA thread, but users were quick to take notes from both it and the second, thus some information lives on.
The combined details contained in both AMAs is extensive. A lot of this seems plausible, some of it is vague enough that a person with no inside knowledge could reliably guess, and a few points stick out as possible red flags indicating that the leak is a hoax, but none are particularly obvious. While parts of this may end up being true, we doubt all of it is legit. As always with leaks, definitely take these details with a pinch of salt.
Regarding the release of the game, the leaker claims that currently October 2023 is the projected launch window. While Rockstar is known for keeping their games in the oven a good long time, this seems a little bit suspicious, considering the time since the launch of GTA 5 has already surpassed any interim period between games in the series prior. Realistically there is no way the game will release this year, granted, but an early-mid 2022 prediction would be more believable. The game will first launch on consoles, with a PC version following it a year later.
Allegedly Red Dead Redemption is being remastered, and that project is taking precedence currently because it is slated to be released before GTA 6. Speaking of Red Dead Redemption, the leaker alleges that RDR2 had a major influence on the direction Rockstar is taking GTA 6 in.
The chapter system will make a return, temporary locations outside the open world will be featured — like Guarma in RDR2 — and the story will take a more emotional tone than previous GTA titles, though not quite as emotional as Arthur's story. In the second AMA, the leaker specified that there will be a linear visit to Liberty City, and also a brief chapter on a Cuban island.