Taylor Swift’s “august” is most specifically classified as dream pop. The song also incorporates guitar pop and soft rock, but dream pop is the clearest single genre answer.
Its classification reflects the recording’s spacious production, blurred textures, reverb-heavy vocals, and floating instrumental layers. Those qualities distinguish it from the country-pop sound of Swift’s early career and from the brighter synth-pop style associated with much of 1989.
Genre labels can overlap, especially for songs built from several production traditions. “august” is therefore also described using guitar pop and soft rock, but those additional labels do not replace its primary dream-pop description in reference sources.