Excludes from federal capital gain the greater of $10M or 10× basis on sale of Qualified Small Business Stock held at least 5 years. Post-OBBBA 2025 (stock issued after July 4, 2025): cap raises to $15M with tiered exclusions at 3-year (50%) and 4-year (75%) holds. Also excluded from the 3.8% NIIT and not an AMT preference item.