Hellfest 2021 has officially been moved to 2021 with mostly the same lineup. Among the bands that did not reschedule were Mastodon, Thy Art is Murder, Meshuggah (because they're working on a new album), The Black Dahlia Murder, Periphery, Body Count, and August Burns Red.
The above bands have so far been replaced by Puscifer, Dropkick Murphys, and Northlane. Expect additional replacements to be announced soon. Hellfest 2021 will take place between June 18 and 20.
