Article mentions that these 330-900 NEO's are for both replacement of older aircraft and for measured growth.
Delta has reached an agreement with Air Lease Corporation (ALC) to lease two new Airbus A330-900neo aircraft set for delivery in the fourth quarter of 2020 and first quarter of 2021. These aircraft will be powered by Rolls-Royce Trent 7000 engines.
"These two incremental aircraft represent an opportunistic play to fulfill our near-term widebody aircraft needs for our customers and employees as older generation aircraft are retired and to support measured growth in 2021,"
With the accelerated 330-900 NEOs deliveries scheduled for next year, 2020 will now see 7 new A330-900 NEO aircraft in the DL fleet.
https://news.delta.com/delta-adding-2-m ... neos-fleet