Glossary
Bundler
In ERC-4337, a node that listens to the UserOperation mempool, packages valid ops into a single transaction, and submits it to the EntryPoint contract on-chain.
Bundlers are the EOAs that actually broadcast account-abstraction
activity to Ethereum. They watch a separate UserOperation mempool,
validate each op locally (simulate against the EntryPoint), and
package valid ones into a regular transaction that calls
handleOps on the EntryPoint contract.
Bundlers compete on inclusion latency and fee revenue from the priority fees attached to each op. Anyone can run one; major infrastructure providers (Pimlico, Stackup, Alchemy, Biconomy) sell hosted bundler services that wallets can plug into.