Dewalt 18v lithium-ion batteries !?

DeWalt DCD970KL
Just saw this while browsing acme tool.
It looks to me like dewalt is making lithium batteries in the old 18v form factor. I can’t imagine a reason other than making them reverse compatible but wondering what other folks know?

I picked up a DeWalt drill/impact combo kit in '09 with those batteries. At the time that was the bee’s knee’s and quite possibly the last “improvement” their 18v line ever saw.

Indeed this is not a new development. I picked up a Lion Dewalt 18V battery and charger about 10 years ago. The new charger is required but it will also charge the old NiCad batteries. In fact, the Lion battery has all but died on me now, hence my switch-over to using B&D 20V Max batteries via adapter.