We reported some time ago that Gearbox was keen to bring cross-play to Borderlands 3, but it was never actually confirmed. Publisher 2K games has been less keen on the idea, stating it was something they were "looking at" and not confirming either way.
It seems now that, at least at launch, there will be no cross-play support. Recently, a tweet from the official Borderlands twitter stating that followers were invited to a "celebration of togetherness" - which many assumed meant cross-play announcements.
It appears this won't be the case, though, as Randy Pitchford has now confirmed that there will be no cross-play support at launch via Twitter.
Some folks may be speculating that this thing tomorrow may be about cross play. Tomorrow’s thing is awesome, but *not* about cross-play. But, Good News: We are committed to supporting cross-play for Borderlands 3 with our partners as soon as practicable after launch. #talklater https://t.co/XtUzrBpySP— Randy Pitchford (@DuvalMagic) July 15, 2019
So it leaves the actual purpose of the announcement open to speculation, but one thing is for sure, cross-play won't be part of the game, at least at launch.
We'll be sure to report on the actual nature of the announcement tomorrow, which will be at 10am eastern time tomorrow.