What The MSSP 2026 Changes Mean For Small ACOs?

Small ACOs have always operated under tighter margins and fewer administrative resources than larger health systems. The MSSP 2026 Proposed Rule adds a new layer of pressure. CMS is accelerating the timeline for risk adoption, revising how beneficiary minimums work, and removing certain quality score adjustments that smaller organizations have relied on. Understanding what changed and what it demands operationally is the first step before performance years begin.

The Push Into Risk Is Getting Faster

The most consequential change in the MSSP 2026 Proposed Rule is the reduction in how long an ACO can stay in a one-sided risk arrangement.

Previously, ACOs could remain in the BASIC track's one-sided model for up to seven performance years. Under the finalized rule, that window has been cut.

CMS will cap participation in the BASIC track's one-sided model to a maximum of five performance years during the ACO's first agreement period, down from the current maximum of seven years. This change applies to agreement periods beginning on or after January 1, 2027.

For smaller ACOs still building infrastructure and care management capacity, this compressed timeline is significant. The gap between understanding risk-based contracts and being financially ready for them is real, and two fewer years to prepare narrows that gap considerably.

Beneficiary Minimum Rules Get More Flexible (With Limits)

On the more favorable side, CMS adjusted how the 5,000-beneficiary minimum is applied. Under the MSSP 2026 Proposed Rule, CMS is easing beneficiary assignment rules by requiring ACOs to meet the 5,000-beneficiary minimum only in the third benchmark year, rather than every benchmark year. This gives smaller and rural ACOs more room to grow their assigned population before facing compliance pressure.

That said, there are conditions attached:

• ACOs that drop 5,000 beneficiaries below in any benchmark year must participate only in the BASIC track
• They face caps on shared savings and losses
• They are excluded from benefits designed for low-revenue organizations
• They cannot participate in the ENHANCED track

So while the flexibility is real, it comes with restrictions that limit what smaller ACOs can access in terms of program benefits and track options.

The Health Equity Adjustment Is Being Removed

Starting performance year 2026, the health equity adjustment (HEA) applied to ACO quality scores will be discontinued.

CMS reasons that other mechanisms already cover similar ground, specifically, the Complex Organization Adjustment, the eCQM/MIPS CQM reporting incentive, and flat benchmarks for Medicare CQMs in their first two performance periods.

For ACOs serving high proportions of dually eligible or low-income beneficiaries, this matters. The HEA was designed to account for the challenges of serving these populations. Its removal shifts the burden of maintaining quality scores to the remaining adjustments, which may not fully compensate in every case.

Beneficiary Assignment Now Includes Behavioral Health Codes

CMS is updating what counts as a primary care service for beneficiary assignment purposes.

Beginning January 1, 2026, new behavioral health integration and psychiatric Collaborative Care Model add-on services will be included in primary care service definitions. This means that they are furnished alongside Advanced Primary Care Management services.

This has a practical upside for ACOs investing in integrated behavioral health. More services count toward assignment, which can improve the alignment between Medicare CQM-eligible beneficiaries and the ACO's assignable population.

Quality Reporting: What's Changing

The MSSP 2026 Proposed Rule carries several quality reporting updates that affect day-to-day operations:

• The APP Plus measure set adds colon cancer screening for 2026
• CMS begins monitoring compliance with the alternative quality performance standard in 2026 and may take enforcement action for ACOs failing to meet either standard
• The CAHPS for MIPS Survey will move to a web-mail-phone protocol beginning with performance year 2027, replacing the current mail-phone method.
• CMS is expanding Extreme and Uncontrollable Circumstances (EUC) policies to cover cyberattacks, including ransomware and malware, effective in 2025

The EUC expansion is worth noting given how frequently healthcare organizations face cybersecurity incidents. ACOs affected by qualifying events can now seek relief on both quality and financial performance calculations.

What Small ACOs Need to Do Now

The combined effect of these changes puts pressure on smaller ACOs to move faster on several fronts. A few practical areas to address:

• Review the agreement period history to determine when the five-year one-sided risk cap will apply to your organization
• Assess beneficiary population size and track eligibility before the next benchmark period
• Confirm quality reporting pathways for Medicare CQMs and eCQMs under the updated APP Plus framework
• Strengthen cybersecurity protocols to ensure eligibility for EUC relief if needed

These are not abstract policy questions. Each one has a direct operational and financial implication.

Final Call

The MSSP 2026 Proposed Rule reflects CMS's broader direction: fewer extended timelines, more accountability, and a faster path into risk-based participation. For small ACOs, that means less runway and more decisions to make in a shorter period.

Managing these transitions requires more than policy awareness. It requires real-time data on assigned populations, quality measure performance, and financial exposure across tracks. Persivia's healthcare platforms support ACOs in building that operational foundation, from data aggregation and care gap identification to quality reporting workflows and population health management. For ACOs navigating the demands of the MSSP 2026 Proposed Rule, having the right infrastructure in place is what makes the difference between reacting to changes and staying ahead of them. 

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