Add Scripps Health in San Diego, Advocate Health Care in Illinois and Mountain States Health Alliance in Johnson City, Tenn., to the growing list of would-be accountable care organization pioneers, or providers that are part of ACOs that have applied for the Centers for Medicare & Medicaid Services Pioneer ACO program.

The applicants I've spoken to recently describe the Pioneer ACO as a more flexible, custom-fit version of the main ACO program, albeit one with room for only 30 participants.

The interest from large, integrated providers in the Pioneer ACO is the latest twist in the two-year-old accountable care rollercoaster, starting with its inclusion as one of the care coordination experiments in the Affordable Care Act.  First came a year's worth of hype that ACOs would usher in a transformation of care delivery by incentivizing hospitals, doctors and other providers through shared savings payments to improve quality and control costs. Then, after the proposed regulations were released in April, came several months of criticism from providers that the program was too financially risky and narrowly defined to entice participation.

Now, the Pioneer ACO program is receiving heightened interest from providers hoping to nab one of those 30 elite spots.  Dennis Vonderfecht, president and CEO of Mountain States Health Alliance, which is applying for the program through its newly formed ACO, has experienced each of those twists and turns personally.

"We initially were very excited about the whole concept of the ACO," Vonderfecht said. "…The excitement kind of got dashed for us, along with everyone else, when all the [regulations] came out, when it was so prescriptive. Once that message got to CMS … and the Innovation Center came out with the Pioneer ACO, we got a little more excited again, because we felt like there was an opportunity to truly have some innovative models."

ScrippsCare in San Diego, an ACO partnership between Scripps Health and North American Medical Management, has also formally applied for the program, Scripps Health CEO Chris Van Gorder told me recently.  Van Gorder, who has been critical of the regulations for the initial ACO program, is hoping Pioneer offers more flexibility for providers, particularly around the attribution of patients. Van Gorder and other industry leaders have called for prospective attribution, where ACOs know beforehand which patients they will be serving, instead of the retrospective attribution proposed in the original program.

"CMS is being fairly flexible in allowing each of the organizations to have some modifications to the rules," Van Gorder said.

David Sensibaugh, vice president for Integrated Solutions Health Network and one of Mountain State's partners in its ACO, told me that CMS is currently vetting applications for the program along with the Department of Justice and the Federal Trade Commission, who are scrutinizing applicants to iron out potential antitrust issues. CMS is then expected to meet with applicants later this month before deciding which ACOs to accept. Vonderfecht and Van Gorder both told me that those conversations will also be critical in informing their organizational decisions as to whether they want to join the program if they receive the green light from CMS.

"We'll find out how flexible they're really going to be," Van Gorder said.

Haydn Bush is senior online editor for Hospitals & Health Networks magazine.