Short answer: A full dual has Medicare plus full Medicaid benefits; a partial dual has Medicare plus only a Medicare Savings Program that helps with premiums and, for QMB, cost-sharing. The difference decides whether Medicaid covers services like nursing home care.
Full-benefit duals have full Medicaid coverage on top of Medicare. Medicare.gov says the state pays their Part B premium, may pay their Medicare cost-sharing depending on their level of Medicaid, and Medicaid may cover services Medicare doesn’t, like nursing home and personal care. In Texas, people 65 and older and adults with disabilities who qualify for Medicaid through SSI or the Medical Assistance Only route get it through STAR+PLUS managed care, which covers acute care and long-term services and supports (1 TAC 353.2).
Partial duals have only a Medicare Savings Program. The Texas HHSC handbook is explicit: someone eligible for QMB alone does not get regular Medicaid benefits, and SLMB and QI people get no Medicaid card.
Why it matters for plan choice: the integrated D-SNP special enrollment period is open only to full-benefit duals, while the monthly Part D change applies to anyone with Medicaid or Extra Help.