The "Expanding Health Care Options for First Responders Act" establishes a new Medicare buy-in option for specific first responders. This option is available to qualified individuals aged 50 to 64 who have separated from service due to retirement or disability, provided they are U.S. residents and not already eligible for Medicare. Those who enroll will receive comprehensive benefits equivalent to Medicare Parts A, B, and D, including the ability to join Medicare Advantage plans. Participants will pay a monthly premium calculated to cover the average per capita costs of all Medicare benefits for this group. The bill ensures that this coverage qualifies as minimum essential coverage under the Affordable Care Act (ACA) and makes enrollees eligible for ACA premium assistance tax credits and cost-sharing reductions. Furthermore, it allows employers to contribute to premiums for retired employees without adverse tax implications and guarantees the issue of Medigap policies upon initial and subsequent enrollment. To oversee implementation, a Medicare Buy In Oversight Board will be established, including representatives from insurers, actuaries, consumer advocates, and first responder communities. The Secretary of Health and Human Services will also award grants for outreach, public education, and enrollment assistance to help eligible individuals understand and access this new option. The bill explicitly states that its provisions should not negatively impact existing Medicare beneficiaries or the Medicare Trust Funds.