Swift features a teaser of a new song in her commercial for Diet Coke. The song is yet to be named, but Swift confirmed it was a new song via her Twitter.
Behold, the Diet Coke ad that depicts my perfect world. Featuring a new song and Olivia, who is now a cat actress. http://t.co/dhzqFTZbkE
— Taylor Swift (@taylorswift13) October 15, 2014