Borderlands 3 has not yet entered development, Gearbox Software founder Randy Pitchford has stressed via Twitter. His statement comes after Borderlands 2's lead writer revealed that the team is currently brainstroming ideas for the next game.
Pitchford took to Twitter to quell rumours, along with the message, "Chill out internet. No one has started working on a sequel to Borderlands 2. It's fun to talk and think, but actual effort is focused on Borderlands 2 DLC, Aliens, etc."
"Clean and Simple truth: The only Borderlands related game development work going on right now is for Borderlands 2. I expect that to change at some point, but that is the state of the box at this moment in time..."
So that's not an out-and-out denial of the Borderlands 2 lead writer's claims that Borderlands 3 is at least being discussed at the studio.