Someone over on the GTAforums going by the alias teapotuberhacker have uploaded what they claimed to be the testing build for Grand Theft Auto VI. The poster claims they obtained the data from Rockstar’s internal Slack group indicating this was an external hack and not coming from someone within Rockstar Games or Take-Two Interactive directly.
Grand Theft Auto titles have had a long history of fake rumors and footage flooding the internet, but this one might finally be the extremely rare exception. Games journalism Jason Schreier took to Twitter to confirmed that after reaching out to some sources at Rockstar Games that the gameplay that leaked online is indeed real.
The footage is from a debugged version which strongly indicates this is an alpha build of the game. The footage is also likely to be at the very beginning of the game as in one of the leaked videos features some notifications pop up acting as an introduction to controls.