Imposes an annual mark‑to‑market tax regime for very high‑net‑worth individuals so unrealized gains are taxed each year instead of being deferred by “buy, borrow, die” strategies. It also closes several loopholes that let wealthy people pass on untaxed gains to heirs and restricts certain deferral elections and tax-free exchange treatments.

Creates a limited three‑year carryback for net marked‑to‑market capital losses, adjusts how several existing tax provisions apply to affected taxpayers, and adds special rules for expatriation and related trusts/entities. Most changes take effect for taxable years beginning after December 31, 2025, with some specific rules phased or keyed to notices and defined dates.