Amtrak will be utilizing NJT and MARC train sets and run them on the NEC as "Event Extras." Those event extras will also be making an extra stop at Hamilton NJT station.
Event Extras running between NYC and Philly will be NJT's, MARC sets will be for trips between DC and Philly
NEC Schedule: http://www.amtrak.com/ccurl/893/771/WMOF-W02,0.pdf
Keystone Schedule: http://www.amtrak.com/ccurl/282/302/WMOF-W10.pdf