Dream pop is the most specific genre associated with Taylor Swift’s “august” in its Wikipedia description.
The song is also described as combining guitar pop and soft rock, but dream pop best captures its hazy atmosphere, reverberant vocals, shimmering textures, and gradual orchestration. These qualities distinguish it from Swift’s earlier country-pop work and from the brighter electronic production of some of her mainstream singles.
The track’s sound was designed to feel cinematic and summery while remaining emotionally wistful. Strings, keyboards, guitars, and restrained synthesizers contribute to its layered arrangement, and the production grows toward a fuller ending.
Genre labels can overlap, so “guitar pop” and “soft rock” are not wholly unrelated descriptions. However, the canonical answer sought here is dream pop, the first genre listed in the song’s infobox.