The GTA 5 source code is leaked and reveals aspects such as that the original ending of each character was more beastly or that there were 8 DLC planned for the story.
Christmas has come to Rockstar Games, it seems that Santa Claus left the company this GTA 5 source
From the screenshots it looks pretty easy to compile:
If they just ripped their entire git repos or something, and it’s complete, it should be pretty easy to compile.
Edit: Compile instructions: https://pastebin.com/igt8BM4S