FAQs by topic:
- Model Purpose
- Model Features
Additional ACO PC Flex technical FAQs (PDF) are also available
Updated June 2025
Model Purpose
What is the Accountable Care Organization Primary Care Flex (ACO PC Flex) Model?
The ACO PC Flex Model is a 5-year voluntary primary care payment model that is being tested within the Medicare Shared Savings Program (Shared Savings Program), which began January 1, 2025. ACOs that participate in the ACO PC Flex Model (PC Flex ACOs) jointly participate in the Shared Savings Program.
The ACO PC Flex Model seeks to reduce program expenditures and improve quality of care and health care outcomes for Medicare beneficiaries through the alignment of financial incentives for primary care, an emphasis on flexibility and primary care innovation, and strong monitoring to ensure that beneficiaries receive access to high-quality, person-centered primary care. The model tests whether alternative payment for primary care services will empower ACOs participating in the Shared Savings Program and their primary care providers to use more innovative, team-based, person-centered, and proactive approaches to care that positively impacts health care outcomes, quality, and costs of care.
The model provides more flexibility in the use of funds for primary care providers, increases resources for primary care, and strengthens incentives for organizations to participate in the Shared Savings Program. This includes, for example, newly formed low revenue ACOs and ACOs that include federally qualified health centers (FQHCs) or rural health clinics (RHCs) as ACO participants.
How does the ACO PC Flex Model support the Innovation Center’s goal to drive participation in accountable care?
The model strengthens incentives for more providers to form ACOs in areas that are underserved and increase the number of people with Medicare who are in an accountable care relationship.
Model Features
How will ACOs and their primary care providers benefit from participating in the ACO PC Flex Model?
Primary care is the foundation of a high-performing health care system and fundamental to improving the health of the United States. ACOs have been limited in their ability to provide advanced primary care because of visit-based payment mechanisms and financial incentives in fee-for-service Medicare. The ACO PC Flex Model tests enhanced and prospective primary care payments to enable more team-based, proactive, and person-centered care by ACOs and their primary care providers. These payments include a one-time Advance Shared Savings Payment and monthly Prospective Primary Care Payments (PPC Payment).
The Advance Shared Savings Payment is intended to cover costs associated with forming an ACO (where relevant) and administrative costs for required model activities. This payment will not be risk adjusted or based on the number of beneficiaries assigned to an ACO. All ACOs will receive the same Advance Shared Savings Payment amount.
How does the ACO PC Flex Model impact Medicare beneficiaries?
Beneficiaries with Original Medicare retain all of their rights, coverage, and benefits, including the freedom to see any Medicare health care provider. Like previous ACO models, ACO PC Flex Model requires ACO participants to make medically necessary covered services available to beneficiaries in accordance with applicable law and prohibits restricting a beneficiary’s freedom to choose where he or she receives care. Even if a beneficiary is assigned to an ACO participating in the ACO PC Flex Model, they always have the freedom to see any Medicare-enrolled provider or supplier.
CMS expects that beneficiaries whose primary care provider is part of an ACO participating in the ACO PC Flex Model will see and feel improvements in the quality and experience of care they are getting because of the ACO PC Flex Model. We The Innovation Center refers to this model test as the ACO PC Flex Model given the flexibility in care delivery enabled by the PPC Payments. This includes flexibility to coordinate primary care delivery and enhance coordination with specialists. The PPC Payment rate is derived from the average county primary care spending and amplified by payment enhancements based on characteristics of the ACO and the assigned patient population. Deriving the rate from average county spending rather than the historical volume of services rendered by an ACO is a critical feature for increasing payment for primary care and supporting flexibility in how services are delivered. The model tests whether this flexibility would improve the beneficiary experience by allowing providers to arrange for services in a manner that best serves Medicare patients and pays for care management, patient navigation, behavioral health integration, and other care coordination services. Moreover, the model's payment design is expected to provide greater access for areas that are medically underserved reaching beneficiaries who have not previously received coordinated care.If at any time a Medicare beneficiary or their caregiver has concerns about the ACO PC Flex Model, the Innovation Center has a model liaison that is part of the Medicare Beneficiary Ombudsman team in the Offices of Hearings and Inquiries. The model liaison can be reached through 1-800-MEDICARE and will assist in facilitating communications with the Medicare Quality Improvement Organizations (QIOs), the CMS regional offices, and ACO PC Flex Model team to ensure the beneficiary’s concerns are heard.
Can beneficiaries opt-out of CMS data sharing with ACOs?
Yes, beneficiaries can opt out of having CMS share their claims data with an ACO PC Flex Model for care coordination and quality improvement purposes at any time by contacting 1-800-MEDICARE and indicating their preference that CMS does not share such data with the ACO.
Eligibility and Participation
Can providers in ACOs participate in other Innovation Center models if they are a part of the ACO PC Flex Model?
Health care providers participating in another Innovation Center model that involves shared savings will not be allowed to participate at the same time in the ACO PC Flex Model, unless otherwise permitted by CMS. Visit the Innovation Center’s model webpage for more information about models focused on other aspects of care.
Is the model affiliated with HRSA’s Medicare Rural Hospital Flexibility (Flex) program?
No. HRSA’s Flex program provides funds to states for technical assistance to Critical Access Hospitals (CAHs). HRSA’s Flex program has no relation to the ACO PC Flex Model.
Can ACOs participating in the ACO PC Flex Model receive Advance Investment Payments (AIP) or Prepaid Shared Savings (PSS)?
ACOs may not participate in the ACO PC Flex Model and also receive Advance Investment Payments (AIP) or Prepaid Shared Savings (PSS) under the Shared Savings Program.
Does this model qualify as an Advanced or Merit-based Incentive Payment System (MIPS) Alternative Payment Model (APM)?
Advanced APM status in the ACO PC Flex Model is consistent with CMS’ Advanced APM determination for each Shared Savings Program risk track, where CMS has determined that Level E of the BASIC track and the ENHANCED track are Advanced APMs for performance year 2025. Eligible providers who are included on the participant list participating in the Level E of the BASIC track or the ENHANCED track will be eligible for Qualifying Quality Program (QPP) Participant (QP) determinations.
What is a low revenue ACO? How does my ACO know if it is low or high revenue?
The Shared Savings Program regulations define “low revenue ACO” under 42 CFR § 425.20 as an ACO whose total Medicare Parts A and B fee-for-service revenue of its ACO participants, based on revenue for the most recent calendar year for which 12 months of data are available, is less than 35% of the total Medicare Parts A and B fee-for-service expenditures for the ACO’s assigned beneficiaries, based on expenditures for the most recent calendar year for which 12 months of data are available. These low revenue ACOs often face greater financial challenges than high revenue ACOs with expanding access to high-quality primary care, because they tend to be less capitalized, more risk-averse, and less likely to take on performance-based risk than high revenue ACOs.
The Shared Savings Program provides revenue determinations to ACOs in the ACO Management System (ACO-MS) as part of the Shared Savings Program application process.
Eligibility for the ACO PC Flex Model will be based on final revenue determinations provided by CMS during phase 1 final dispositions in October.
What is the model timeline?
The ACO PC Flex Model will be tested over five performance years, from January 2025 – December 2029. Performance years will occur in the calendar years of 2025, 2026, 2027, 2028, and 2029, respectively. A Shared Savings Program ACO participating in the ACO PC Flex Model will start a new Shared Savings Program agreement period and will enter into a new Shared Savings Program participation agreement for the performance years January 2025 through December 2029. In addition, the ACO will have a separate ACO PC Flex Participation Agreement for performance years January 2025 through December 2029.
Will there be another application cohort in the future?
At this time, CMS will not have an additional application round. For more information on upcoming CMS innovation Center models, please visit our Innovation Models page.