Over the course of a professional career that spanned more than 40 years, Tom Petty released a vast amount of material, including 13 albums with the Heartbreakers, three solo outings, two with Mudcrutch and dozens if not hundreds of covers, outtakes, live versions, stray B-sides, Petty songs covered by other artists, and more.

Yet there’s a lot of unreleased music inside the late musician’s vault, and four CDs of it will be coming in a boxed set called “American Treasure” scheduled for release on Sept 28, it was announced on the Petty channel on SiriusXM Tuesday. The set, featuring artwork by Shepard Fairey, will include previously unreleased live and studio material, alternate versions — 60 songs in total, compiled by Petty’s daughter Adria, his wife Dana, longtime Heartbreakers Mike Campbell and Benmont Tench and veteran Petty engineer Ryan Ulyate. It dates from the beginnings of the Heartbreakers to recent years, which presumably would make the set a collaborative release between Universal (which owns the rights to Petty’s early material issued on Shelter or Backstreet/MCA Records) and Warner Music, which released his music from 1994 on. More details will be released Wednesday morning, which was teased by a countdown clock on Petty’s website beginning earlier this week.

The set was previewed on SiriusXM with an unreleased song dating from 1982 called “Keep a Little Soul” (not to be confused with the 1967 hit by the Music Explosion, “Little Bit O’ Soul,” which Petty and the Heartbreakers performed live).

Considering the length of “American Treasure,” it seems likely that it could include the second disc of an expanded version of the 1995 album “Wildflowers” that was announced in 2015 but has not been released. The sessions for that album, the first of three Petty recorded with producer Rick Rubin, spawned a bounty of material that did not make the original album, some of which emerged on the “She’s the One” soundtrack the following year. In 2015 Petty dropped a song called “Somewhere Under Heaven” as the lead track for the 20th anniversary double-album expanded edition, titled “Wildflowers: All the Rest.”

Petty died on Oct. 2 of last year of an accidental overdose of a variety of medications, according to a post written by his widow, Dana, and eldest daughter, Adria. According to a statement from the Los Angeles County Department of Medical Examiner, obtained by Variety, the musician was taking several medications, including Fentanyl, oxycodone, Xanax, Restoril, and Celexa. In their statement, Petty’s family named a litany of health problems the musician faced, “including emphysema, knee problems and most significantly a fractured hip.” The hip injury worsened, the family explained, while Petty was on his final tour, which ended just a week before his death.

“On a positive note we now know for certain he went painlessly and beautifully exhausted after doing what he loved the most, for one last time, performing live with his unmatchable rock band for his loyal fans on the biggest tour of his 40 plus year career,” the family’s message said. “He was extremely proud of that achievement in the days before he passed.”