This idea was abandoned due to issues with the engine, specifically with how the weapons and armor would work.

The game was originally slated to have three playable races - human, ghoul, and super mutant. They used development tools for a few months before they were given the source code, which let them dive in to deeper development. The team initially did not have access to the source code until Bethesda cleared the security of it. Obsidian submitted a three-page pitch to Bethesda for the project, which they named ' Fallout: Sin City.' The game was later renamed to ' Fallout: New Vegas.' East Coast, Obsidian set the game in the American West. It was specifically designed to be more of an expansion rather than a sequel Obsidian, however, saw the project as akin to the Grand Theft Auto titles Vice City and San Andreas - not numbered entries, but still full games in their own right. They knew the game would not be a direct, traditional sequel to Fallout 3, and it was referred to as ' Fallout 3.5' within Obsidian. Discussions for New Vegas began between Obsidian and Bethesda in 2008/09.

New vegas steam mods