Bundlers and mempools

Smart wallets do not submit UserOperations directly to Ethereum validators. They send them to bundlers — specialized operators that collect UserOps from an alternative mempool, simulate them for profit, and package winners into a single regular transaction.

Multiple bundlers can run in parallel, similar to block builders in the MEV supply chain. Wallets may send UserOps to several bundlers to improve inclusion speed. Decentralized bundler networks aim to reduce single-point censorship, though today most flow passes through a handful of operators.

Bundlers get paid from the wallet's EntryPoint deposit or from paymaster sponsorship. Understanding this economics matters for dApp developers — underpaying gas limits can leave UserOps stuck while competitors' operations confirm first.