The new tracks are called Patient Zero, Cleveland!, Pink Clouding and Babylon.
Taylor explained that the songs were not left over from the original album. She wrote them after travelling to Sweden to celebrate its success with producers Max Martin and Shellback.
“Really we just wanted to reflect and take in how grateful we were for the moment we were in,” Swift wrote on her Instagram.
“But there was a studio there and we did what we do when we feel anything at all: We wrote more songs.”
A music video for Patient Zero will be shown at the MTV Video Music Awards on Sunday.
At the ceremony, Taylor Swift will become the first person to receive MTV’s new Artist Director award, which celebrates musicians who help direct their own videos.