Bethesda’s Peter Hines has confirmed that a fourth Fallout is in the works.
“We didn’t buy the Fallout franchise to just do Fallout 3 and then stop,” Hines said.
“But let’s get this one out of the door before we worry about the next one.”
Obviously by the quote, no details have been released on “Fallout 4″–only that it will exist at some point in the future.
Source: [TechRadar]

