The CY2027 Proposed Rule for MSSP ACOs: What Changes, What It Pays, and Where We Stand

For Shared Savings Program ACOs, the 2027 Physician Fee Schedule proposed rule is the most consequential fee schedule rule in years. Below is each proposal that touches an ACO, what it changes operationally, and the position our comment letter took.

This is the ACO companion to our summary of the full rule. Conversion factors, specialty impacts, the proposed MIPS sunset, and the Ambulatory Specialty Model provisions are on the proposed rule hub page.

PY2027: The APP Plus Measure Set Drops to Eight Measures

CMS proposes to remove measure 305 (Initiation and Engagement of SUD Treatment) and measure 493 (Adult Immunization Status) from the APP Plus set beginning PY2027. Neither measure has ever been reported: under current policy, 305 enters the set in 2027 and 493 in 2028 or later. In practice, this cancels the SUD reporting build ACOs would otherwise need before January, including new-episode identification and the 14-day initiation windows, and it takes the immunization data work behind 493 off the roadmap with it.

Our comment letter supported the removal. Both measures would have required substantial data infrastructure before either had shown it could be reliably reported at the ACO level, and 493 depends on an eCQM specification that still does not exist. Nothing currently measured goes away, and the remaining eight measures stay aligned with the Universal Foundation.

PY2027: MIPS CQMs Survive, and a New Medicare eCQM Collection Type Arrives

The collection-type proposals could shape every ACO's PY2027 reporting strategy. First, CMS proposes to extend the MIPS CQM collection type and its reporting incentive beyond PY2026, when both are currently set to end, which removes the forced conversion to the remaining collection types. Second, CMS proposes a new “Medicare eCQM” collection type: it mirrors the existing eCQM specifications but runs the measure population against the ACO's assigned beneficiary list instead of the all-payer, all-patient population the existing eCQM type requires. The Medicare eCQM and Medicare CQM collection types would be scored on flat benchmarks, and for measures 001, 134, and 236 the flat benchmark would apply retroactively to 2026 when reported via Medicare CQMs. ACOs retain the ability to mix collection types across the five clinical quality measures.

The catch sits in one sentence of the rule: Medicare eCQMs would be ineligible for the Complex Organization Adjustment and the reporting incentive available to the existing eCQM collection type. The option could solve the all-payer aggregation problem at the cost of scoring support, and whether that trade pays differs from one ACO to the next.

We supported both proposals and objected to the exclusion. The ACOs that most need an assigned-population option are multi-TIN, multi-EMR organizations, the same ones the Complex Organization Adjustment exists to support. CMS says the adjustment compensates for the complexity of all-payer reporting, but for these ACOs the hard part is aggregating data across many TINs and EMRs, and that burden is the same for a Medicare-only population. Our letter asked CMS to extend the adjustment to Medicare eCQMs.

Our platform models the collection-type trade-off per ACO before the reporting period opens. We are running it for our ACO clients now; if you want yours run, ask us.

PY2026: Data Completeness Relief

Beginning with PY2026, an ACO could exclude a participant TIN from a measure's submission under specified circumstances, such as an unexpected practice closure or a specialty EMR that cannot support the measure, provided the remaining TINs cover at least 95% of assigned beneficiaries. The 75% data completeness requirement would still apply to each measure submitted, and the relief covers all four collection types.

This was one of the headline support items in our letter, because today a single TIN's reporting failure, often for reasons outside the ACO's control, can cost the whole organization its quality performance standard. We asked for one change: “other circumstances as determined by CMS” needs defined criteria and a predictable process, because relief an ACO cannot count on in advance becomes an audit argument after the fact.

PY2027: The CEHRT Use Requirement Is Restructured

CMS proposes to sunset the requirement that ACOs report all MIPS Promoting Interoperability measures starting in PY2027. In its place, an ACO would complete one of three activities: report at least one of the five clinical measures via eCQM or Medicare eCQM; report at least one measure using CEHRT and attest to using a FHIR-based API through a certified Health IT Module; or attest to one ACO-level metric (e-prescribing, health information exchange, or patient electronic access), each built as “at least one provider in every participating TIN,” with allowable TIN exclusions documented for audit.

An ACO that lands on Medicare eCQMs above satisfies the first option automatically, which is the cleanest path. The rule also includes a request for information on applying electronic prior authorization to ACOs in future years; nothing is required yet, but it signals alignment with the electronic prior authorization requirements arriving on the MIPS side.

The restructuring is real simplification, and we supported it. Our letter also asked for concrete configuration guidance and vendor conformance review in the final policy: EMR vendors interpret CEHRT requirements differently, and the audit exposure for a per-TIN attestation sits with the ACO, not the vendor.

PY2026: Enforcement Relief on the Current CEHRT and PI Requirements

The proposed rule also extends CMS's PY2025 enforcement discretion on the MSSP Promoting Interoperability reporting requirement to PY2026. CMS states that it will not take compliance action against an ACO that does not meet the current CEHRT use and related PI requirements for PY2026, and that there is no impact on the ACO's ability to earn or receive shared savings. Because this is enforcement discretion rather than codified regulation, the underlying requirements stay on the books for PY2026; CMS is forgiving noncompliance without deleting the obligation.

PY2027: The Financial Methodology Package

CMS is proposing six changes to how benchmarks and shared savings are calculated. In plain terms:

• The sharing rate for BASIC Level E ACOs is proposed to increase from 50% to 60% of gross savings. The downside is proposed to remain at 30%.
• The regional benchmark weight is proposed to be reduced from 50% to 35%. ENHANCED track ACOs whose spending runs below their regional average would get a smaller benchmark boost from that difference. Higher-spending ACOs and the entire BASIC track are unaffected.
• The prior savings adjustment is proposed to increase from 50% to 75%. When CMS rebases a benchmark, the ACO's own earned savings have lowered its historical spending and drag the new benchmark down; this adjustment adds a portion of prior savings back. At three quarters instead of half, an ACO gives back less of its benchmark for having performed well.
• The 5% cap on upward benchmark adjustments is proposed to become risk-adjusted. ACOs with sicker populations get more headroom, because the cap would reflect actual case mix instead of treating every population as average.
• A new growth adjustment to the benchmark is proposed for ACOs that recruit clinicians and beneficiaries new to value-based care. It adds an upward benchmark adjustment for expanding the program's reach.
• A guardrail is proposed to keep the ACPT within 1 point below and 1.5 points above actual national growth. One third of the annual benchmark update is a forecast fixed years in advance, and when it under-projects, ACOs lose savings through no fault of their own, as recent cohorts did.

The Level E and regional adjustment changes apply only to agreement periods beginning on or after January 1, 2027, so existing ACOs would see them at renewal rather than mid-agreement. Applications for a January 1, 2027 start have already closed; CMS plans to give those applicants a time-limited window after the final rule to change their BASIC or ENHANCED selection, and an ACO that did not apply would next enter a new agreement period on January 1, 2028.

The ACPT guardrail also moves the calendar: CMS is delaying PY2025 financial reconciliation. Results are now planned for November 2026, with payments in December. CMS proposes to apply the guardrail's lower bound retroactively to ACOs that started in 2024 through 2026, and it is holding the PY2025 run until after the final rule so the correction can be applied. By CMS's own description, every ACO covered by the retroactive fix either benefits from it or is unaffected.

Track also decides QP status: only BASIC Level E and ENHANCED count as Advanced APMs, so only participants in those tracks can reach QP status and the higher QP conversion factor. Per the rule, 74% of MSSP ACOs are already in those two tracks.

Our letter supported the package as the first serious attempt in a decade to stop ACO benchmarks from falling because the ACO performed well. We reserved our position on the regional adjustment reduction, which for a lower-spending ENHANCED ACO is a benchmark cut at renewal. If that describes your ACO, model the cut against your current benchmark before you decide when to renew.

CY2027: G2211 Becomes Two Payment Modifiers, and the Second One Is ACO-Only

CMS proposes to retire the G2211 add-on code, currently a flat payment of roughly $16, and replace it with two modifiers on qualifying office and outpatient E/M visits. The first adds 16% to the base E/M payment and is available to all practitioners. The second adds 32% and is available only to practitioners on an MSSP ACO participant list (any track or level) or in the new LEAD model; participant-list status is the only requirement. It can be billed for every Medicare patient the practitioner treats, not just assigned beneficiaries, and G2211's longitudinal-care criteria carry over, so ongoing management of a serious or complex condition qualifies, including the chronic-condition specialist relationships that drive attribution in many ACOs.

One limitation carries over from G2211: neither modifier is payable on a visit billed with modifier 25 alongside a procedure (annual wellness visits, vaccines, and Part B preventive services are the only exceptions), so same-day office procedures earn no modifier. CMS sought comment on whether to relax this for global-period procedure days, and our letter addressed it.

To make the stakes concrete, here is the stacked 2027 impact for an illustrative office-based practice:

*Assumptions: $1M in Medicare allowed charges; roughly 2,400 visits qualifying for the longitudinal modifier at an average base E/M payment of ~$115; roughly 300 same-day E/M-plus-minor-procedure encounters. QP status is available only in Level E or ENHANCED, only when the clinician clears the year's statutory thresholds, and, as proposed, only at the participating TIN. Actual results vary with E/M share and same-day procedure patterns.

The same illustrative practice swings from a $21,500 loss outside an ACO to a $22,600 gain inside one, and nearly all of that comes from participant-list status alone; QP status adds the last $4,900.

For the ACO itself, there is a second-order effect worth planning for. The modifier claims count in assignment calculations, benchmarks, and performance-year spending. In the early years, the added spend hits performance-year expenditures before benchmarks reflect it; we estimate that transition effect at 0.3 to 0.5% of total cost of care. Against minimum savings rates of 2.0 to 3.9%, that is a meaningful piece of the savings hurdle in the early years.

Whatever the final rule does with administration, audit current G2211 utilization across your participants before January. Under-billing today becomes twice as expensive under a percentage structure.

Additional Provisions Worth Knowing

Approved ACOs could reduce or eliminate beneficiary Part B cost sharing through participant arrangements, targeted to start April 1, 2027; used well, that is a screening follow-through tool for measures 112 and 113. Beneficiary notification simplifies to a single standardized notice due by May 30. On assignment, advance care planning, SBIRT, and vaccine adverse effects management codes join the definition for PY2027, and beginning PY2028, primary care billed through non-ACO TINs would be excluded. On CAHPS there is nothing new; the web-mail-phone administration finalized last cycle takes effect for PY2027 as planned.

CMS also used requests for information to float larger changes. One solicited comment on prospective primary care payment within MSSP, the largest structural change the program has contemplated since inception. A second asked how to better integrate specialty care into the program, including attribution, benchmarking, and specialist performance measurement; CMS notes specialists are 65% of participating physicians and roughly 80% of Part B physician spend. If your ACO's attribution runs through specialists, that RFI is effectively about your model.

What to Do Before the Final Rule

CMS tends to revise collection-type mechanics and modifier administration between proposed and final rules in response to operational comments, so plan 2027 for more than one outcome. If any of these proposals would hit your ACO, tell us what you are seeing. For the numbers behind the decisions here (the collection-type trade-off, the modifier expenditure effect, or your own participants' G2211 audit), our APP Plus quality reporting and contract analytics run those models now.