Uniswap v4 launched January 31 2025 introducing customizable hooks cutting gas costs up to 99.99 percent. Live on Ethereum, Polygon, Arbitrum, OP Mainnet, Base, BNB Chain, Blast, World Chain, Avalanche, Zora Network. Developers attach solidity logic to swap lifecycle through hooks. Logic executed before and after pool creation, liquidity operations, swaps, donations. Most significant AMM upgrade since V2.