"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Apple Launches 27" iMac 3TB Hard Drive Replacement Program
Apple is contacting affected iMac owners that provided a valid email address during product registration to inform them about the new replacement program. iMac owners can check if they are affected by entering the computer's serial number on Apple's support website, and visit the Genius Bar, locate an AASP or contact Apple Technical Support to initiate the replacement process.
Apple advises that customers who paid to have their hard drive repaired contact the company for a refund. The replacement program covers affected iMac models until December 19, 2015, or three years from the affected iMac's original date of sale, depending on whichever is longer. Read about the iMac replacement program on Apple's support website for further details.
Apple announced a similar replacement program in mid-2011 for select 21.5-inch and 27-inch iMacs sold between May and July of that year with Seagate 1TB hard drives that could also fail under certain conditions, later expanding the program to include a much broader timeframe. That replacement program expired on July 23, 2013 after being extended for a year. Apple also launched a repair program for early MacBook models in 2010.