No fourth producer is credited alongside Taylor Swift, Jack Antonoff, and Joe Alwyn on “august.”
The song’s listed producers are Swift, Antonoff, and Alwyn. This makes the question a precise credit check rather than a question about every producer associated with Folklore. Antonoff created the initial instrumental, while the track was completed within the album’s collaborative production process.
Aaron Dessner is the most likely mistaken answer because he was central to Folklore’s production and songwriting. He produced many of the album’s songs and participated in the Grammy-winning album project, but he is not listed as a producer of “august.”
Joe Alwyn used the pseudonym William Bowery for some songwriting credits elsewhere on Folklore, but “august” specifically lists Alwyn by name among its producers. The distinction between album-wide collaborators and track-specific credits matters here.