Update:
Delta has confirmed its Delta One Club lounges will be exclusive to Delta One business class passengers, without access for even top-tier Diamond Medallions. This was
sorta expected, as it's in line with United's Polaris lounges, but also
sorta-not given American's Flagship lounges are open to top-tier Aadvantage and Oneworld frequent flyers.
https://www.executivetraveller.com/d...b-lounge-guide