True to Gearbox’s word, the game seems to be banking on cross-play functionality.
When Gearbox boss Randy Pitchford recently commented on the possibility of Borderlands 3 declaring exclusivity for the Epic Games Store on PC, he mentioned that if that were to happen (it did end up happening), it would happen because of how Epic has been pushing for functionalities such as cross-platform play, which, according to Pitchford, holds a lot of importance for the upcoming looter shooter.
New evidence seems to suggest the same. On Borderlands 3’s Microsoft Store page, among its capabilities is listed “cross-platform co-op”. Co-op, of course, is supremely important in a game like Borderlands 3, and the possibility of shared pools of players across platforms raises its potential even further. The assumption here would be that cross-play features are across Xbox One and PC, and not Xbox One and PS4 (since that just seems to be the trend).
There’s also no knowing right now whether the PS4 version of the game will also have cross-play with PC- but it very well may do so. Though Sony has been reluctant to enable cross-play in games with the Xbox One and the Switch, they’ve been quite open to doing so for PC versions of games for plenty of time now.