Three accountable care organizations have left the Centers for Medicare & Medicaid Services’ Next Generation model less than one year into the program.

The program began in January with 21 ACOs; after the departures of Heritage California ACO, Pennsylvania-based River Health ACO and WakeMed Key Community Care in North Carolina, that number has dropped to 18. Despite the dropouts, the number of ACOs participating still falls within the 15 to 20 organizations CMS thought would join, Modern Healthcare reported.

The ACOs that have left the model cited concerns over the cost-saving requirements and risk of loss posed by the program. The River Health ACO, which dropped out in February, left after realizing the ACO would not meet the cost saving targets set as part of the program.

Those hard-to-reach savings were what spurred many ACOs in the Pioneer program to leave — the program dropped to just half of its original cohort of 32 organizations late last year. Some went on to join the Next Generation model, which carried more risk of loss to providers but also benefits such as telehealth and skilled nursing waivers.

The 18 remaining ACOs are expected to stick with the program for now; a new round of participating ACOs is set to be announced in August.