This fall, CMS is expected to finalize updates to the Medicare Shared Savings Program (MSSP) that will take effect in 2027. The proposals aim to expand participation, tighten oversight, and refine quality reporting, all while shortening the timeline for new ACOs to take on risk. For organizations in MSSP or considering entry, the changes are worth close attention.

The Barrier to Entry
One of the most significant proposals would relax the beneficiary attribution threshold in the early years. Currently, ACOs must have at least 5,000 assigned beneficiaries in all three Benchmark Years (BYs). Starting in Performance Year (PY) 2027, CMS is proposing that the 5,000 threshold would only apply in BY 3. Smaller or new ACOs could enter with fewer beneficiaries in BY 1 and/or BY 2.

However, these entrants would face guardrails:

• Limited to the BASIC track.
• Shared savings/losses capped using an alternative calculation.
• Certain low-revenue ACOs would lose the ability to share in savings without meeting the Minimum Savings Rate (MSR).

Although this change could open the door for smaller provider groups, leaders will need to assess whether the capped upside offsets the benefit of earlier entry.

Real-Time Oversight on Ownership Changes Today, updates to an ACO’s certified participant list happen only once a year. Starting in PY 2026, CMS proposes that ACOs must:

• Report certain Changes in Ownership (CHOW) for participants and skilled nursing facility (SNF) affiliates during the performance year.
• Specifically, report when a surviving TIN has no prior Medicare billing history.

The operational impact of this proposal is twofold. By requiring mid-year reporting, CMS would help ensure patient attribution and quality reporting remain uninterrupted, even when ownership changes occur. For SNF affiliates, it also preserves access to the valuable 3-day rule waiver during transitions. However, this added flexibility comes with a higher bar for internal governance. ACOs will need robust monitoring systems to detect and document CHOWs in real time, ensuring compliance without disrupting performance.

Shifts in Quality Scoring
In addition to lower barriers to entry and real-time CHOW documentation, two proposals would reshape the APP Plus quality measure set:

• Remove the health equity adjustment (currently worth up to 10 bonus points for meeting certain criteria). While only a small number of ACOs benefited, its removal reflects a broader pivot away from DEI-linked scoring.
• Drop the Screening for Social Drivers of Health (SDoH) measure. This would reduce administrative work but also scale back structured SDoH data collection.

What This Means for ACO Strategy As described, the proposed changes signal a “faster, leaner” MSSP model.

• Faster: Shorter time in upside-only models means new entrants must prepare for downside risk sooner.
• Leaner: Quality scoring will focus more narrowly, with less emphasis on health equity-specific metrics.
• More agile: Real-time participant list updates will require operational readiness.

For ACO leaders, understanding and acting on next steps could be the difference between winning and falling behind. After giving careful attention to the CMS proposed updates, ACO leaders should consider:

• Evaluating readiness to move to two-sided risk within five years.
• Building internal processes for mid-year participant updates.
• Reviewing quality strategies in light of removed measures and scoring changes.

The bottom line is, CMS is creating a pathway that’s more accessible on day one, but less forgiving over time. The winners will be those who enter with a plan to scale infrastructure, master attribution, and adapt quickly to evolving quality frameworks.

Learn more about CMS’s proposed rule for CY 2026 here.