Medicare Shared Savings Program (MSSP)

CMS assigns Medicare fee-for-service beneficiaries using primary care services, as defined in the program regulations. The October 31, 2025 Physician Fee Schedule final rule fact sheet says that for the performance year starting January 1, 2026, and later years, that definition includes new behavioral health integration and psychiatric collaborative care management add-on services when they are furnished with advanced primary care management services. CMS kept G0136 in the definition, with the updated descriptor for a physical activity and nutrition assessment.

The guidance page also states an exclusivity rule. An ACO participant TIN (Taxpayer Identification Number, the billing entity) that has a specialty used in assignment and bills Medicare for primary care services must be exclusive to one Shared Savings Program ACO. An individual National Provider Identifier (NPI) may participate in more than one ACO if the clinician bills under more than one TIN.

The same guidance page states the long-standing rule that an ACO must have at least 5,000 assigned Medicare fee-for-service beneficiaries in each benchmark year. The October 31, 2025 final rule changes that for agreement periods beginning on or after January 1, 2027, described below.

The October 31, 2025 final rule fact sheet (CMS-1832-F) finalizes these Shared Savings Program changes. For agreement periods beginning on or after January 1, 2027, an ACO that is inexperienced with performance-based risk may stay in a one-sided model of the BASIC track for up to 5 performance years in its first agreement period on the glide path, instead of up to 7 performance years across two agreement periods. By a second or later agreement period, that ACO participates in BASIC Level E or the ENHANCED track. An ACO with fewer than 5,000 assigned beneficiaries in benchmark year 1, benchmark year 2, or both may not enter the ENHANCED track.

For those same agreement periods, an ACO must still have at least 5,000 assigned beneficiaries in benchmark year 3, and may have fewer than 5,000 in benchmark year 1, benchmark year 2, or both. An ACO in that position may enter only the BASIC track, and shared savings and shared losses are capped at a lower amount if any benchmark year is under 5,000. CMS also removed the health equity adjustment to an ACO's quality score beginning in performance year 2026. Beginning with performance year 2027, the CAHPS for MIPS patient experience survey (Consumer Assessment of Healthcare Providers and Systems, for the Merit-based Incentive Payment System) uses a web, mail, and phone protocol.

The July 14, 2026 proposed rule fact sheet (CMS-1848-P) is not a final rule. It proposes a BASIC Level E sharing rate of 60 percent, a lower cap on the ENHANCED track's positive regional adjustment (35 percent instead of 50 percent), a higher prior-savings scaling factor (75 percent instead of 50 percent), and a risk-adjusted cap on upward benchmark adjustments. Most of its assignment methodology changes would apply for the performance year starting January 1, 2028. It does propose adding codes for screening and brief intervention, vaccine adverse effects management, and advance care planning to the primary care services used for assignment for the performance year starting January 1, 2027. Treat those items as proposals until CMS issues the final rule.

The Medicare Shared Savings Program is the permanent ACO program in Original Medicare. ACO REACH is a CMS Innovation Center model. CMS's ACO REACH page says it runs for performance years 2023 through 2026, performance year 2026 is the last year, and CMS is not taking new applications for the rest of the model. CMS names the LEAD model as the successor, announced to run from January 1, 2027, through December 31, 2036.

ACO REACH offers Professional risk at 50 percent of savings and losses and Global risk at 100 percent, with capitated payments. MSSP uses the BASIC track, including a glide path from one-sided risk, and the ENHANCED track. CMS's July 14, 2026 proposed-rule fact sheet describes the current ENHANCED sharing rate as 75 percent and BASIC Level E as 50 percent. An organization can be in MSSP or in ACO REACH. The TIN exclusivity rule on the Shared Savings Program guidance page applies to MSSP, not to REACH.

CMS compares the ACO's Medicare fee-for-service spending for assigned beneficiaries with a benchmark. If spending is under the benchmark and the ACO meets the quality standard, the ACO shares in the savings at the track's rate. On a two-sided track, spending over the benchmark can produce shared losses at that same rate, up to a cap.

CMS's July 14, 2026 proposed-rule fact sheet describes the current ENHANCED sharing rate as 75 percent and the BASIC Level E rate as 50 percent. It proposes, and has not finalized, a Level E rate of 60 percent and a lower cap on the ENHANCED track's positive regional adjustment, 35 percent instead of 50 percent. The benchmark's regional adjustment is that cap. Treat the July figures that the fact sheet marks as proposals as proposals until the CY2027 Physician Fee Schedule final rule is published. CMS's regulation index still lists CMS-1848-P, the July 16, 2026 proposed rule, and not a CY2027 final rule.

Shared savings require the ACO to meet the program's quality performance standard. The October 31, 2025 Physician Fee Schedule final rule fact sheet says CMS removed the health equity adjustment to an ACO's quality score beginning in performance year 2026. Beginning with performance year 2027, the CAHPS for MIPS survey uses a web, mail, and phone protocol.

The quality score is not a separate product from the savings calculation. An ACO that misses the quality standard does not share in savings for that year, even when spending is under the benchmark. The measure set and the reporting method are the ones CMS publishes for that performance year on the Shared Savings Program guidance page.

An ACO applies to CMS. The Program Guidance and Specifications page says that for agreement periods beginning on July 1, 2019, and later, participation is at least five years, on the BASIC track or the ENHANCED track. A participant TIN that has a specialty used in assignment and bills Medicare for primary care services must be exclusive to one Shared Savings Program ACO. An NPI may be in more than one ACO when the clinician bills under more than one TIN.

The same page states the long-standing rule of at least 5,000 assigned Medicare fee-for-service beneficiaries in each benchmark year. The October 31, 2025 final rule changes that for agreement periods beginning on or after January 1, 2027: fewer than 5,000 is allowed in benchmark year 1, benchmark year 2, or both, only if benchmark year 3 has at least 5,000, and only on the BASIC track, with a lower cap on savings and losses. Application instructions and the annual deadline are on the CMS Shared Savings Program application page, not on this definition.