Crypto glossary
Upgradeable proxy contract
An upgradeable proxy contract keeps a fixed address and stored data but forwards calls to a separate logic contract that its admin can replace with new code.
Smart contract code cannot be edited once deployed, so developers use a workaround. Users interact with a proxy, which holds the balances and other storage and passes every call to an implementation contract using a special instruction called delegatecall. To upgrade, the admin points the proxy to a new implementation; the address and data stay the same while the behaviour changes. Common patterns include transparent proxies, UUPS and beacon proxies, with standard storage slots defined in EIP-1967.
Most large DeFi protocols, stablecoins and bridges use proxies so they can fix bugs and add features without migrating users. Explorers flag proxy contracts and show which implementation is active, and risk reviewers check who controls upgrades, whether changes pass through a timelock, and whether a multisig or governance vote is required.
Upgradeability is a trust trade-off. Whoever holds the upgrade key can replace the logic with code that drains funds, and stolen admin keys have caused major losses. Proxies also bring technical risks such as storage layout collisions and uninitialised implementation contracts.
Example
A stablecoin issuer upgrades its token through a proxy to add a new compliance feature; holders keep the same balances and address, but the code behind them changes overnight.