Titled Fallout New Vegas, it's being developed by Obsidian Entertainment (Neverwinter Nights 2, Star Wars Knights of the Old Republic II) with PC, PS3, and Xbox 360 versions planed for a simultaneous launch in 2010.
New Vegas will be an RPG in the style of Fallout 3, Bethesda noted, but the company did not confirm if it uses the same engine. The studio also stressed that it approached Obsidian to make a new Fallout entry, not the other way around.
"It is not a sequel to Fallout 3," said Bethesda marketing VP Pete Hines. "It was just a great opportunity we thought to work with some guys who very clearly know Fallout--Feargus [Urquhart] and those guys were there in the early days of Fallout."
Obsidian Entertainment was founded in 2003 by several former employees of Black Isle Studios, the company responsible for the original Fallout titles.
"We approached them. And obviously they were like, 'Yeah!' That was a pretty easy conversation," Hines continued. "It's definitely an RPG. Same sort of experience as what folks got in Fallout 3. It's not Fallout Tactics, it's not Brotherhood of Steel."
"It's another Fallout game in that universe."
Obsidian is planning to release its espionage-based RPG Alpha Protocol later this year. The studio was also working on an RPG set in the Aliens universe until early this year, when it was revealed to be cancelled.
"[New Vegas] has no impact whatsoever on what [Fallout 3 director] Todd Howard and his guys are working on [internally at Bethesda]," added Hines.
For more on Fallout New Vegas, check out our interview with Mr. Hines.