How long did GISS climate modeling suggest Venus might have sustained oceans in its ancient past?

For up to two billion years

Climate modeling conducted by NASA's Goddard Institute for Space Studies (GISS) provided scenarios suggesting a significantly long period of potential habitability in Venus's distant history. These models explored conditions where Venus accumulated water vapor similarly to Earth, resulting in simulations showing the planet maintaining oceans and a mild climate for an extended period, estimated at up to two billion years. This optimistic view posits a long, temperate beginning before a catastrophic shift to the planet's present inhospitable state. This duration contrasts sharply with more recent research suggesting a much faster transition away from habitability.