Short answer: Texas Insurance Code 1652.059 and 1652.060 (added in 2025 by HB 2516) require Medigap insurers to offer under-65 Texans on Medicare because of ESRD or ALS the same plans they sell at 65, guaranteed issue during the six months starting the first month of Part B, with price limits.
During that six-month window the insurer cannot deny or condition coverage, medically underwrite, charge more for health status, impose a waiting period or exclude pre-existing conditions.
Pricing: Plans A, B and D must be offered at the same premium charged to a 65-year-old. Every other plan, including Plan G, can cost no more than 200 percent of the age-65 premium for that plan (200 percent of the rate, not 200 percent more).
This is broader than the rule for other under-65 disabled Texans, who are guaranteed only at least one plan. Federally, people with ESRD can also join Medicare Advantage plans, so compare both, especially dialysis center and transplant networks.