Luke Bryan and Dierks Bentley are out as ACM Awards co-hosts after two years. Luke hosted the show three times alongside Blake Shelton prior to that. It's not clear who will be filling in as 2018 hosts, or if Luke may be hosting by himself or with another co-host.
Historically a long list of people have hosted the ACM Awards including Reba McEntire, Dolly Parton and Vince Gill. The very first ACM Awards were in 1966.