How many ACO models are there?

There are two main current Medicare Accountable Care Organization (ACO) program types active through the Centers for Medicare & Medicaid Services (CMS), alongside several past or specialized demonstration models.

Active Main Medicare ACO Programs

• Medicare Shared Savings Program (MSSP): The permanent, largest nationwide program with hundreds of participating ACOs offering different tracks for sharing savings and losses.
• ACO REACH Model (Realizing Equity, Access, and Community Health): An active CMMI innovation model launched in 2023 (replacing Direct Contracting) focused on underserved populations, featuring Professional and Global risk-sharing options.

Specialized / Recent Active Initiatives

• ACO Primary Care Flex (PC Flex) Model: Tests a specialized primary care payment design built alongside the Shared Savings Program.
• Kidney Care Choices (KCC) Model: Focuses specifically on accountability for patients with chronic kidney disease and end-stage renal disease.

Past CMS Innovation Models

CMS has previously tested and concluded several other demonstration models, including:

• Pioneer ACO Model
• Next Generation ACO Model
• Advance Payment ACO Model
• ACO Investment Model (AIM)
• Global and Professional Direct Contracting (GPDC) Model (re-branded into ACO REACH)

Accountable Care Organization (ACO) models are value-based healthcare frameworks where groups of doctors, hospitals, and other health care providers team up to give coordinated, high-quality care to patients while lowering costs.

The Centers for Medicare & Medicaid Services (CMS) and other payers run several primary ACO models with different financial risk levels and target populations.

Major CMS ACO Programs & Models

• Medicare Shared Savings Program (MSSP): The permanent, largest federal program featuring progressive tracks (Basic and Enhanced levels) that allow providers to share in the savings they generate or face financial penalties under two-sided risk.
• ACO REACH (Realizing Equity, Access, and Community Health): A model focusing on health equity and underserved communities that offers Professional (lower risk) and Global (higher risk) participation arrangements, alongside capitated payment options.
• ACO Primary Care Flex Model: A voluntary model designed for low-revenue MSSP ACOs to introduce prospective primary care payments to support small or independent practices.
• Legacy/Past Innovation Models: Earlier pilot tests by the CMS Innovation Center—such as the Pioneer ACO Model, Next Generation ACO Model, and Direct Contracting—paved the way for today’s risk-sharing structures.

Organizational Structures of ACOs

Aside from payment rules, organizations form different structural types depending on their makeup:

• Physician-Hospital Organizations (PHOs): Formed by hospital medical staff and the hospital itself.
• Multispecialty Group Practices: Integrated groups of diverse clinical specialists.
• Independent Practice Associations (IPAs): Separate physician practices uniting strictly for contract purposes.
• Federally Qualified Health Center (FQHC)-Led ACOs: Centered around community health centers serving low-income populations.

There are 511 active Accountable Care Organizations (ACOs) participating in the Medicare Shared Savings Program for 2026, alongside other specialized federal models.

Breakdown of Medicare ACO Programs (2026)

• Medicare Shared Savings Program (MSSP): 511 participating ACOs serving 12.6 million people.
• ACO REACH Model: 74 participating ACOs serving 1.7 million beneficiaries.
• Kidney Care Choices Model: 74 participating entities serving 237,000 beneficiaries.
• ACO Primary Care Flex (PC Flex) Model: 23 participating ACOs serving 359,720 beneficiaries.

In total, across all federal initiatives, millions of traditional Medicare beneficiaries are covered, and commercial or private-market tracking puts the total active U.S. count even higher (with commercial and independent trackers like Definitive Healthcare noting over 1,800 total public and private entities).

Yes, the ACO REACH Model is scheduled to end on December 31, 2026, marking the conclusion of its four-year performance period.

Transition to the LEAD Model

• Replacement: The Centers for Medicare & Medicaid Services (CMS) Innovation Center is launching the Long-term Enhanced ACO Design (LEAD) Model to take its place.
• Timeline: LEAD begins on January 1, 2027, and is structured as a 10-year initiative running through 2036.
• Focus: The new model aims to support smaller independent providers, rural practices, and organizations serving complex or dually eligible beneficiaries.

Key Considerations for ACOs

• Final Year Adjustments: Performance Year 2026 brings updated risk score caps and adjusted regional benchmark weightings under CMS Guidelines.
• Alternative Pathways: Organizations not transitioning to LEAD are evaluating shifts to the permanent Medicare Shared Savings Program (MSSP) or other commercial options.

The primary downside of an Accountable Care Organization (ACO) is the potential for downside financial risk and heavy administrative burdens if patient care costs exceed expected targets.

Financial and Administrative Disadvantages

• Financial Penalties: Under two-sided risk models, if the ACO fails to lower overall healthcare spending below the assigned benchmark, providers must pay money back to the insurer or Medicare.
• High Upfront Costs: Joining or setting up an ACO requires expensive investments in health information technology, electronic health records, data analytics dashboards, and care coordination staff.
• Increased Bureaucracy: Providers often face extra reporting requirements, quality metrics tracking, and administrative red tape that can distract from direct patient care.

Operational and Clinical Challenges

• Loss of Autonomy: Physicians may feel their clinical freedom is restricted by institutional guidelines, utilization reviews, or network-preferred referral patterns.
• Complex Management: Aligning incentives, corporate cultures, and policies across large networks of independent doctors, specialists, and hospitals is difficult and prone to friction.
• Data and Privacy Hurdles: Sharing extensive patient data across different provider systems creates technical barriers and privacy management challenges.