CMS-HCC V28 at 100% in 2026: What Coders Must Know

The Three-Year Transition Is Over

For the past three years, risk adjustment coders have been living in a hybrid world. The Centers for Medicare and Medicaid Services (CMS) phased in its new Hierarchical Condition Category (HCC) model -- Version 28 (V28) -- gradually, blending it with the legacy Version 24 (V24) model to give health plans time to adjust. Payment year 2024 used a 67/33 split favoring V24. Payment year 2025 flipped it to 33/67. Now, as of January 1, 2026, V28 stands alone at 100 percent.

There is no more safety net. Every diagnosis code you submit, every Risk Adjustment Factor (RAF) score calculated for a Medicare Advantage (MA) beneficiary, and every audit finding from this point forward runs entirely through V28 logic. If your coding workflows, documentation practices, or provider education programs were built around V24 assumptions, the time to finish adapting is not next quarter. It is now.

What Changed: The Numbers That Matter

The structural differences between V24 and V28 are significant, and they affect daily coding decisions in concrete ways.

Fewer codes map to HCCs. CMS removed approximately 2,000 International Classification of Diseases, 10th Revision, Clinical Modification (ICD-10-CM) diagnosis codes from HCC mappings. The total dropped from roughly 9,797 codes in V24 to approximately 7,770 in V28, a shrinkage confirmed by the official CMS 2026 model software and ICD-10 mappings release. That means codes your team may have been capturing for years -- codes that previously drove RAF scores -- no longer count. For a broader walkthrough of the V28 category restructuring, see AAPC's CMS-HCC model V28 overview.

HCC categories were reorganized. The number of payment HCCs changed from 86 under V24 to 115 under V28, split across 26 condition families. Some categories were merged, some were split into more granular groupings, and several were eliminated entirely. For example, the interaction between immune disorders (formerly HCC 47) and certain cancers (HCC 8 through 12) was removed.

Specificity requirements increased. V28 was designed to reward precise clinical documentation and penalize vague coding. A diagnosis of "vascular disease" that might have mapped under V24 may require documentation of "peripheral vascular disease with ulceration" or "peripheral arterial disease with gangrene" to qualify under V28. The bar for what counts is meaningfully higher.

Why This Matters More Than You Think

With fewer codes in the model, each remaining code carries proportionally more weight. A single unsupported or incorrectly assigned HCC has a bigger impact on a plan's overall risk profile than it did under V24. The margin for coding error has contracted at the same time that audit scrutiny from CMS, the Office of Inspector General (OIG) -- whose work plan tracks trends and patterns across the V24 and V28 models -- and Risk Adjustment Data Validation (RADV) programs has intensified.

Consider the financial stakes: CMS estimated that V28 would reduce MA risk scores by 3 to 8 percent across the industry. For large health plans managing hundreds of thousands of beneficiaries, that translates to tens of millions of dollars in reduced revenue -- unless documentation and coding practices rise to meet the new standard. MedPAC's February 2026 comment letter on the CY2027 Advance Notice reinforced that the agency intends to continue tightening risk-adjustment accuracy even after V28 stabilizes.

The plans that prepared early are already seeing results. Those that treated the phase-in period as a grace period rather than an implementation window are now facing a gap between what their providers document and what V28 actually recognizes.

High-Impact Areas Coders Should Focus On

Not all HCC families were affected equally. Some clinical areas saw dramatic changes that demand immediate attention from coding teams.

Diabetes with complications. Under V28, the linkage between diabetes and its manifestations must be explicitly documented. Coding diabetes with chronic kidney disease (CKD), for instance, requires the provider to clearly state the causal relationship in the medical record. Simply listing both conditions on the problem list is not sufficient. The documentation must show that the diabetes is causing or contributing to the kidney disease to support the appropriate HCC assignment.

Heart failure staging. V28 introduced more granular distinctions for heart failure. Coders must ensure that documentation reflects the specific type (systolic, diastolic, or combined), the acuity (acute, chronic, or acute-on-chronic), and any associated conditions. Generic references to "congestive heart failure" without further classification may not map to the intended HCC.

Chronic kidney disease staging. CKD stages 1 through 3 were always lower-value from a risk adjustment perspective, but V28 further refined how these stages interact with other conditions. Documentation of the exact stage, along with any qualifying complications, is essential.

Substance use disorders and mental health. Several behavioral health conditions were reclassified under V28. Coders working with psychiatric documentation should verify that the codes they have been using still map to active HCCs and that the documentation supports the level of specificity now required.

Vascular disease. As noted above, vascular conditions require far more specificity under V28. Peripheral artery disease, chronic venous insufficiency, and related diagnoses need detailed documentation of severity, laterality, and complications to map correctly.

Documentation Is the Entire Game

Every conversation about V28 eventually comes back to the same point: the model only works if the documentation supports it. The Monitor, Evaluate, Assess, and Treat (MEAT) criteria remain the gold standard for demonstrating that a condition was actively addressed during a face-to-face encounter.

Under V28, the consequences of weak documentation are amplified. A condition that was "addressed" only by appearing on a problem list, without any evidence of clinical evaluation or treatment planning during the visit, is unlikely to survive a RADV audit. And with CMS resuming RADV audits for payment year 2020 and beyond -- with new audit cycles launching approximately every three months -- the odds of an audit touching your organization's data are higher than ever.

Coders should work closely with clinical documentation improvement (CDI) specialists and provider education teams to ensure that:

Practical Steps for Coding Teams

If your organization has not yet completed its V28 transition, here is a prioritized action list:

Audit your current code set against V28 mappings. Identify every ICD-10-CM code your team commonly submits and check whether it still maps to an HCC under V28. The encoder is a fast way to verify individual codes, and the full CMS ICD-10-CM code set is the authoritative source for any code in question. Flag any codes that lost their mapping and communicate the changes to your coding staff and providers immediately.

Update your query templates. If your CDI team uses standardized queries to prompt providers for additional documentation, those queries need to reflect V28 specificity requirements. A query that asks "Does the patient have heart failure?" should now ask for type, acuity, and staging.

Recalculate RAF scores using V28-only logic. If your organization has been running parallel V24/V28 calculations during the transition, it is time to retire the V24 column entirely. Use the RAF calculator to model scenarios under pure V28 weights and identify beneficiaries whose scores dropped significantly.

Retrain on high-impact condition families. Focus provider and coder education on the clinical areas listed above -- diabetes complications, heart failure, CKD, behavioral health, and vascular disease. These are the categories where V28 diverges most sharply from V24 and where the revenue impact is greatest.

Verify provider credentials and encounter validity. With the proposed ban on unlinked chart reviews for payment year 2027, the connection between a valid face-to-face encounter and every submitted diagnosis code is more important than ever. Use the NPI lookup to confirm that rendering providers are properly credentialed for the services documented.

Looking Ahead

V28 at full implementation is not the end of the story. CMS has signaled through its 2027 Advance Notice that further payment accuracy measures are coming, including the proposed exclusion of unlinked chart review diagnoses from RAF scores. The OIG continues to publish compliance guidance targeting MA plans, and RADV audit activity is accelerating.

For coders and coding managers, the message is clear: the era of broad code capture with minimal documentation is over. V28 rewards precision, penalizes vagueness, and leaves less room for error than any prior model. The AAFP's physician-facing HCC reference is a useful starting point when re-educating providers on how their documentation drives risk-adjustment outcomes. Organizations that invest in documentation quality, coder education, and compliance infrastructure now will be positioned to thrive. Those that do not will face shrinking revenue and growing audit exposure.

HCC Buddy was built to help coders navigate exactly this kind of transition. Whether you need to check a code's V28 mapping in the encoder, look up a CRC reference for condition categories, or calculate projected RAF scores, the tools are designed to save you time and reduce errors during the most consequential period in risk adjustment coding in years. If you are not already using these resources, sign up and see how they fit into your workflow.