Red Dead Redemption's Legends and Killers Pack is available to download from Xbox Live and PlayStation Network.
It costs 800 Microsoft Points (£6.85) on Xbox Live and $9.99 / £7.99 on PlayStation Network.
Legends and Killers doubles the amount of competitive multiplayer territories with nine new map locations that are weapon-balanced specifically for multiplayer.
New locations vary from the "fog-filled riverside at Thieves' Landing" to the "modern metropolis of Blackwater".
Eight classic "personalities" from 2004's Red Dead Revolver return as multiplayer characters, including Red Harlow, Jack Swift, Annie Stoakes and Shadow Wolf.
The Tomahawk, a new projectile weapon, is available in competitive multiplayer, free roam and single-player modes.
And, of course, there are new Achievements and Trophies to earn.
"With Legends & Killers we wanted to provide a wealth of new content for fans of Red Dead Redemption," said Rockstar Games founder Sam Houser.
"We took care to pick out areas that were unique and exciting and then polished them to provide the best possible multiplayer experience."
Legends and Killers is the first of four packs of RDR add-on DLC to be released over the next few months.