The Zac Brown Band have released three studio albums, each of which sold at least one million copies, as well as their 2013 EP, 'The Grohl Sessions, Vol. 1' with Foo Fighters frontman Dave Grohl. But while the band has enjoyed plenty of success in country music, they aren't about to repeat the same formula for their upcoming project.

"We're all continuing to grow up and get better as musicians, and the chemistry as a band continues to deepen," Zac Brown tells Rolling Stone Country. "Our boundaries have dissolved, and we're going to still do things that are somewhat familiar that people like, but we're also going to stretch out and take chances beyond what we've done before. Some people are going to be really surprised."

The group is planning on spending the remainder of the year working on the still-untitled project.

"All we're doing is recording," Brown adds. "We've got 18 strong songs that we've whittled down and gotten ready. But you never know; one might pop up."

Meanwhile, ZBB's first greatest hits package, 'Greatest Hits So Far ...,' was released Nov. 10. The album includes 14 of their biggest songs, including their debut single 'Chicken Fried,' from 2008, and their duet, 'As She's Walking Away,' with Alan Jackson. The group co-wrote all of the songs on the record, which Brown says is the only way they will ever release music.

“We’re not just going to take some songs from a focus group in Nashville, where people are sitting around in a circle having appointments trying to write catchy songs so they can sell them to a band like us,” he says. “You can tell all our songs come from us and from our artists, the people we write with and travel with. You can hear us in them, and you can hear the chemistry in our band because we live together as a band."

Order 'Greatest Hits So Far ...' here.