CY 2027 OPPS/ASC Proposed Rule, CMS-1850-P

In the CY 2027 OPPS/ASC proposed rule (CMS-1850-P, fact sheet July 2026), CMS proposes removing 637 services from the Inpatient Only list on January 1, 2027 and adding 618 of them to the ASC Covered Procedures List. The remaining roughly 801 more complex procedures would move in CY 2028, completing full IPO elimination by January 1, 2029. Comments are due August 31, 2026.

This is not a trial balloon. It is the scheduled second step of the IPO elimination policy CMS finalized in the CY 2026 OPPS/ASC final rule. The direction is now fixed in regulation: the Inpatient Only list is going away, and the only open questions are which codes move in which year and what conditions attach to them. For revenue cycle teams on both sides of the site-of-service line, the planning clock started in July 2026, not January 2027.

637Services proposed for removal from the Inpatient Only list, effective CY 2027

618Of those services proposed for addition to the ASC Covered Procedures List

~801More complex procedures slated to move in CY 2028

Jan 1, 2029Target date for full IPO elimination

The dated timeline every revenue cycle leader should pin up

CY 2026 Final Rule

The policy is locked in

The CY 2026 OPPS/ASC final rule finalizes the multi-year elimination of the Inpatient Only list. CY 2027 is the first large-volume tranche under that framework.

July 2026

CMS-1850-P released

The CY 2027 OPPS/ASC proposed rule and CMS fact sheet name the numbers: 637 services off the IPO list, 618 onto the ASC Covered Procedures List.

August 31, 2026

Comment deadline, you are here

The last chance to tell CMS which codes, conditions, or timing need adjustment. ASC operators and hospital service lines with clinical concerns about specific procedures should file now.

January 1, 2027

The 637 move

If finalized, 637 services leave the IPO list and 618 become ASC-billable. Payer prior-auth grids and medical policy will lag this date, which is where the denial risk concentrates.

CY 2028

The complex tranche

The remaining roughly 801 more complex procedures move off the list, per the phase-out sequence described in CMS-1850-P.

January 1, 2029

Full IPO sunset

The Inpatient Only list is eliminated. Site of service for the affected procedures becomes a clinical judgment and payer-policy question, not a Medicare list question.

Where the 637 codes actually land

637services removed from the Inpatient Only list, CY 2027

➞

618 proposed for the ASC Covered Procedures List: billable in the ambulatory surgery center setting for Medicare for the first time

19 by arithmetic are removed from the IPO list without a proposed ASC listing, leaving the hospital outpatient department as their outpatient setting

For ASCs, 618 newly coverable procedures is one of the largest single-year expansions of the billable surgical universe the setting has ever been offered. Every one of those codes needs a chargemaster entry, a cost and device-intensity review, coverage verification, and a prior-authorization pathway before the first case is scheduled. For hospitals, the same list is a re-underwriting exercise: hundreds of codes that were automatically inpatient now require documented medical necessity for the inpatient site of service, and utilization review criteria, physician advisor workflows, and case-mix forecasts all have to be re-run.

The Q1 2027 denial window

Commercial and Medicare Advantage prior-authorization grids will not update in lockstep with the Medicare list on January 1, 2027. Expect a window where a procedure is Medicare-payable in an ASC while a payer's own auth grid still classifies it as inpatient only. Claims submitted into that gap draw site-of-service and authorization denials that are winnable but expensive. The mitigation is boring and effective: verify each payer's written policy per code before scheduling, capture the auth reference on every case, and route the first months of claims for these codes through focused pre-bill review.

Operator to-do list before January 1, 2027

ASC revenue cycle teams

Pull the CMS-1850-P addenda and map the 618 proposed ASC codes against your specialty mix and block schedule
Model facility-fee economics per code, including device-intensive procedures, before committing OR time
Build chargemaster, coding, and claim-edit support for every code you intend to perform
Contact each contracted payer in writing for site-of-service and prior-auth policy on the new codes; file the responses
Stand up a pre-bill review queue for the new code set covering the first quarter of 2027
File a comment by August 31, 2026 if specific codes raise clinical or payment-rate concerns

Hospital and health system teams

Re-run medical-necessity and site-of-service logic for all 637 codes; inpatient status must now be supported case by case
Update utilization review criteria and physician advisor escalation paths before the effective date
Refresh patient-status and Two-Midnight documentation training for the affected service lines
Forecast the case-mix and revenue shift as commercial payers follow Medicare's site-of-service signal
Coordinate with any affiliated ASCs on which of the 618 codes migrate and when
Prepare for the CY 2028 tranche now; roughly 801 more complex procedures follow one year later

Sources

CY 2027 OPPS/ASC proposed rule, CMS-1850-P, and the accompanying CMS fact sheet, July 2026. Comments due August 31, 2026.
CY 2026 OPPS/ASC final rule, which finalized the Inpatient Only list elimination policy this proposal continues.

Get ahead of the 618-code wave

ASP-RCM Solutions builds the payer-by-payer authorization grids, chargemaster mappings, and pre-bill review workflows that turn a regulatory list change into clean first-pass claims. Whether you run an ASC absorbing new procedures or a hospital re-underwriting inpatient status for 637 codes, our team can have your CY 2027 playbook ready before the final rule drops.

Talk to our CMS payment team