To add some additional detail:

While other federal agencies can and do administer some of America's 123 National Monuments, about 70% are administered by the National Park Service (NPS); 95% are administered by a Department of Interior agency, including the NPS. Since most are created on existing Federal lands, whichever agency was administering the lands beforehand usually ends up administering the monument, though there are exceptions.

In this case it is clearly going to be an NPS-administered unit. I think it'll be their second largest unit in New England, after Acadia.