More likely than not "no hardware" but I wouldn't bet on it.
This argument rolls around every year.
"Apple never announces hardware at WWDC"
...except for all the times that Apple has announced hardware at WWDC (e.g. 2005, 2013, 2019 Mac Pros, 2017 iMac Pro, M2 chip + M2 MBA, Apple Vision Pro...)
The only things near-guaranteed to be announced at WWDC keynote are new versions of MacOS/iOS/iPadOS/WatchOS but if it makes sense for them to launch hardware they will - especially if something needs pre-announcing to get developers on board. Look at the MR roundups for upcoming products and your guess is as good as anybody else's.
Least likely is any new iPhone - that's more or less a fixed feast for September.
Macs and iPads tend to appear in October/November or Feb/March, but that's less predictable.
Important to distinguish between the developers conference which is - well, exactly what it says, and the opening keynote which is a big press jamboree.