Jimbo Hart, the co-founding bassist of Jason Isbell and the 400 Unit, has officially left the band, which he confirmed on social media today (November 27). “I’m grateful for all the years, all the faces I’ve played for in the course of the band’s history and proud of all we accomplished,” he posted on X.

In June, Hart announced that he was taking a leave of absence from the group, citing a need to tend to his mental health and “resolve some old-school traumas.” As Isbell and the 400 Unit have toured in support of the Grammy-nominated Weathervanes, multiple guest musicians have assumed Hart’s bass duties, among them Anna Butterss and Cat Popper.

Hart has worked closely with Isbell across much of the songwriter’s post–Drive-By Truckers career, a collaboration that’s grown out of the friendship they date back to 2006. In addition to Weathervanes, Hart had played on every other 400 Unit album.