Gearbox president Randy Pitchford confirmed at PAX West 2017 that 90% of his staff were working on a new title, and while it could be Battleborn 2, most of the gaming community is confident it's Borderlands 3. The game has been rumored to be in development for quite awhile and while Gearbox isn't outright confirming that's the game they're making, they aren't necessarily brushing off any suggestions either. Pitchford gave the reasoning for not confirming what game the company is working on in the quote below:

“a product does not exist until it’s announced,”

I would argue that, in the case of video games, it isn't a product until it's completed development, but even that doesn't appear to be a limitation anymore. Who's excited for the imminent announcement of Borderlands 3?

Source: VG247