Gearbox's Randy Pitchford has said not to expect an SDK to be released for Borderlands 2; however, he fully encourages the modding community to start mucking around with the game once it's released.
Speaking during a development session at Rezzed, Pitchford said at one time, releasing modding tools for Borderlands was considered, but in the end, the team felt it best to start on another entry in the franchise.
"There was a moment after Borderlands shipped where we thought about releasing an official SDK," said Pitchford, "but we found that most of what we would be able to do, was already accomplished by the gaming community."
Members of the community had hacked into the game files in Boderlands and allowed for various weapon customization and tools which Pitchford said "was already ahead of what the firm would have been able to do."
"The best thing we could do for the community was get to work on Borderlands 2," he said. "Imagine if we'd spend a year working on an SDK for BL2."
Still, Pitchford hopes the community will take it upon itself to once again create user tools for BL2 as with the first game. He said the team at Gearbox was rather impressed with what was accomplished, and even popped in on occasion and offered some pointers.
So, while an SDK for Borderlands 2 won't be released by Gearbox, just look to your local modding community for support.
Borderlands 2 is out in September on PC, PS3, and Xbox 360.