Medicare Advantage (MA) supplemental benefits have become an increasingly important component of the program, accounting for an estimated $80 billion in plan payments in 2025. Yet little is known about how these benefits are used, partly because they have not been consistently identifiable in encounter data. The Centers for Medicare & Medicaid Services (CMS) interpreted its long-standing encounter data reporting requirements as applying to supplemental benefits, although earlier guidance did not explicitly state this and the reporting system did not accommodate many supplemental services. In 2024, CMS updated the encounter data reporting system and issued guidance intended to make supplemental benefit claims easier for MA organizations to submit and researchers to identify and analyze. This brief examines the first year of available encounter data to assess whether supplemental benefits can be identified and what the results imply for ongoing transparency and accountability efforts.

Key Takeaways

We identified several key findings about the availability and usefulness of the new 2024 supplemental-benefit encounter data:

• CMS established a new supplemental-benefit reporting framework in 2024, including Supplemental Benefit Service Category (SBSC) codes intended to identify supplemental benefits in encounter data.
• The 2024 MA encounter data files available through ResDAC and the Chronic Conditions Warehouse (CCW), Virtual Research Data Center do not contain the SBSC indicator field associated with the new reporting framework.
• Searches within procedure code data fields, Healthcare Common Procedure Coding System (HCPCS) data fields, and other coding fields found no evidence of reported SBSC codes in the currently available 2024 encounter data files.
• We identified approximately 2 million encounter records that appear consistent with supplemental-benefit reporting based on CMS reporting instructions, but the absence of SBSC identifiers made it impossible to determine which supplemental benefits were provided.
• CCW staff subsequently indicated that supplemental-benefit reporting did not begin until September 2024, that reporting during 2024 was highly incomplete, and that supplemental-benefit indicator fields are expected to be incorporated into research files beginning with the 2025 encounter data release.

Policy Implications

Recent regulatory initiatives, stakeholder recommendations, and legislative proposals have emphasized the need for greater transparency and accountability in MA. The 2024 encounter data experience suggests that CMS’s efforts to clarify and strengthen supplemental benefit encounter data reporting requirements are only first steps toward those goals. Meaningful oversight depends not only on requiring plans to submit information, but also on monitoring reporting compliance, validating data quality, and making key data elements available to support independent evaluation. Without access to the SBSC indicator fields or a public assessment of reporting completeness and data quality, researchers and policymakers cannot independently evaluate the implementation of the new reporting framework. Because the supplemental-benefit indicator fields are not currently available in data files available to researchers and are expected to be added in a future encounter data release anticipated in the first quarter of 2027, independent evaluation of CMS’s attempts to improve supplemental-benefit reporting may lag implementation by several years. Although CMS has taken an important step by providing a clear framework for supplemental-benefit reporting, the usefulness of the new reporting framework for transparency and oversight will ultimately depend on whether researchers and policymakers can access the data necessary to independently evaluate implementation, reporting quality, and benefit utilization. As policymakers consider future transparency reforms, the 2024 experience suggests that reporting requirements alone may be insufficient absent mechanisms to monitor compliance, validate reporting quality, make relevant data available for research, and encourage complete and accurate reporting.