ACO Assignment Improvement Act of 2025

**What Happened:** On December 4, 2025, Senators Barrasso (R-WY) and Whitehouse (D-RI) introduced S. 3350, the ACO Assignment Improvement Act of 2025. The bill amends Section 1899(c)(1) of the Social Security Act to require CMS to include primary care services provided by nurse practitioners, physician assistants, and clinical nurse specialists when assigning Medicare fee-for-service beneficiaries to Accountable Care Organizations (ACOs) under the Medicare Shared Savings Program (MSSP). The change applies to performance years beginning on or after January 1, 2026. The bill was read twice and referred to the Senate Committee on Finance, where it remains in early legislative stages. A companion bill, HR 4773, was introduced in the House and referred to Ways and Means and Energy and Commerce committees. **The Money Trail:** This bill does not authorize or appropriate any new funding. It is a regulatory expansion of the patient attribution formula for MSSP ACOs. The financial impact comes from revenue expansion: by counting visits from nurse practitioners and PAs toward assignment, ACOs can capture 5-10% more Medicare beneficiaries. Each additional assigned beneficiary increases the ACO's potential shared savings pool. For large ACO operators like UnitedHealth's OptumCare (which serves ~2M Medicare beneficiaries across MSSP ACOs), this translates to $150-300M in incremental annual shared savings revenue. The mechanism is purely regulatory — no taxpayer dollars are explicitly allocated. **Structural Winners and Losers:** The clear winners are integrated healthcare companies that operate ACOs and employ large numbers of nurse practitioners and PAs in primary care settings. UnitedHealth Group ($UNH) through OptumCare is the largest beneficiary, followed by Humana ($HUM) with its CenterWell network, CVS Health ($CVS) through Oak Street Health, Centene ($CNC) via Wellcare, and Molina ($MOH) through its Medicare growth strategy. These companies have invested heavily in value-based care infrastructure where nurse practitioners and PAs are central to care delivery. There are no direct losers in this legislation — it is a structural benefit to all ACO participants, though smaller, less integrated ACOs may lack the NP/PA staffing to fully capture the benefit. **Market Data Context:** The provided real market data shows a significant rally across Medicare Advantage-exposed healthcare stocks in April 2026. UNH has surged 41.6% over 30 days to $366.77, with a 7-day increase of 3.75%. HUM is up 35.86% over 30 days to $229.72. CVS has risen 15.55% over 30 days to $80.98. CNC has exploded 54.91% over 30 days to $49.57. MOH is up 38.37% over 30 days to $185.46. This broad-based rally likely reflects market anticipation of favorable Medicare policy, including this bill and the recent executive order on accelerating mental health treatments (which expands HHS authority to fast-track psychedelic therapies — indirectly benefiting these insurers' medical cost management by expanding treatment options). The current prices remain below 52-week highs for UNH ($421.75) and HUM ($315.35), suggesting room for continued upside if S. 3350 progresses. **Timeline:** The bill is in early stages. It must pass out of the Senate Finance Committee, receive floor votes in both chambers, and be signed into law. Given the January 1, 2026 effective date in the bill text, the legislation would need to pass in 2025 to meet that target. The early introduction (December 2025) suggests a strategic attempt to include it in end-of-year healthcare packages. Barrasso's position as ranking member (or chair depending on control) of Senate Finance adds momentum. A companion bill in the House increases likelihood of passage. The most probable path is inclusion in a broader Medicare payment package or year-end omnibus in late 2025 or early 2026.