The Uniswap Protocol is an open-source protocol for providing liquidity and trading ERC20 tokens on Ethereum. It eliminates trusted intermediaries and unnecessary forms of rent extraction, allowing for safe, accessible, and efficient exchange activity. The protocol is non-upgradable and designed to be censorship resistant.
There are currently three versions of the Uniswap protocol. V1 and V2 are open source and licensed under GPL. V3 is open source with slight modifications, which are viewable here. Each version of Uniswap, once deployed, will function in perpetuity, with 100% uptime, provided the continued existence of the Ethereum blockchain.