It wasn’t specific in the 7/29 TWAB. It just says Console (with Stadia).
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From what I know, yes they will. Old gen will face new console gen players (good luck with that btw). Pve will be crossplay 24/7 for all platforms. That makes sense since pve is just for giggles anyway. Pc players should probably prepare to see extremely sluggish moving guardians on pve, those guys are most likely the old gen running at 30 fps lol.