The new album was produced by The Black Keys' Dan Auerbach, has earned praise from Paste, American Songwriter, the Tennessean, Nashville Scene and All Music Guide.

Letters In The Deep finds Cadillac Sky embracing broader classical, rock and pop influences, while harkening back to the roots of traditional bluegrass—when albums were made with the players standing around a single mic. Lead singer/mandolin player Bryan Simpson explains, "These days, bluegrass is recorded in a separate room with people behind glass. And that's not the bluegrass that we love. The rawness is missing. We played all the songs just sitting around together, and at the core of every song is a truly live recording."

Dan Auerbach oversaw production duties for the album with a hands-off approach, allowing the music to come together naturally. Auerbach challenged the band to embrace the "here and now" and under his direction, Cadillac Sky would have to make decisions on the fly when tracking and fixing issues in the mix wouldn't be possible. Simpson adds, "Dan encouraged us to just be with our music. He told us not to overanalyze, to let the songs be what they were going to be."

Of the album, Auerbach says, "They rose to the occasion. There are really beautiful sounds on Letters In The Deep. It is as much of a living album as it is an art piece and I'm definitely proud to have my name attached to this project. Whatever genre it is, it's a really great album, and I'm happy that I got to make it."

Based in Nashville by way of Texas, Cadillac Sky is comprised of Bryan Simpson (vocals, mandolin, guitar, violin), Matt Menefee (banjo, upright piano, drums, glockenspiel), David Mayfield (guitar, percussion), Ross Holmes (mandolin, melotron, violin) and Andy "Panda" Moritz (piano, percussion, bass).