Grand Theft Auto Online is live now on Xbox 360, VideoGamer.com can confirm. The PlayStation 3 version is also reported to be live.
Players can access the online multiplayer mode by downloading a 59MB Title Update for GTA 5 and selecting the fourth character on their character selection wheel.
GTA Online is a 16-player multiplayer mode that lets players team up to take on heists, challenge others in races, or engage in shoot-outs.
Players are also able to purchase properties, vehicles and weapons using in-game money, or purchase microtransaction cash packs to boost their bank balance.
Rockstar has previously warned that players should expect to find "crashes, glitches and crazy bugs" in the first few weeks of launch while it tweaks the service.