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ERC-4337: Bundlers, Paymasters, Entry Point

How ERC-4337 implements account abstraction without changing the Ethereum consensus protocol, and the off-chain infrastructure (UserOperations, bundlers, paymasters, the EntryPoint contract) that makes it work.

40 min · expert · part of Account Abstraction & Wallet Engineering

Account Abstraction Without Forking Ethereum

By 2020, Ethereum had been trying to ship protocol-layer account abstraction for years. The first serious attempt, ERC-2938, would have required validators to accept a new transaction format and would have changed how gas accounting worked at the consensus level. It became clear that any change to the consensus protocol would take years of coordination, would conflict with the simultaneous push to merge proof-of-stake, and would risk creating client incompatibilities that could split the network. Account abstraction kept getting deferred. In September 2021, Vitalik Buterin, Yoav Weiss, Dror Tirosh, and Shahaf Nacson published ERC-4337 with a radical insight: you can implement account abstraction entirely outside the consensus protocol. The consensus layer continues to know nothing about smart accounts. Instead, a parallel infrastructure of off-chain "bundlers" collects user requests and submits them to a single trusted smart contract called the EntryPoint, which orchestrates the validation and execution of smart-account operations. The chain itself does not need to change. Validators do not need to upgrade. The standard ships as a smart-contract deployment and a piece of off-chain software, not as a hardfork. The EntryPoint v0.4 deployed on Ethereum mainnet on March 1, 2023, and ERC-4337 has been the dominant smart-account standard on EVM chains ever since. It has been iterated through v0.6, v0.7 (released in April 2024), and v0.8, with each version improving efficiency, signature aggregation, and developer ergonomics. This lesson walks through every piece of the architecture so you can read a UserOperation, understand what a bundler does, and reason about paymaster economics.

Also in this lesson

  • The UserOperation: A New Kind of Transaction
  • The EntryPoint Contract
  • Bundlers: The New Mempool
  • Paymasters: The Economics of Gasless UX
  • Aggregators and Version History

Key terms

ERC-4337
The Ethereum standard for account abstraction without consensus changes, proposed by Vitalik Buterin, Yoav Weiss, Dror Tirosh, and Shahaf Nacson in September 2021 and deployed to mainnet on March 1, 2023. Implements smart accounts through a separate mempool, off-chain bundlers, and the EntryPoint singleton contract.
UserOperation
The pseudo-transaction data structure at the heart of ERC-4337. Contains sender, nonce, callData, gas limits, optional paymaster info, and a signature blob that the sender account knows how to verify. Lives in the alt-mempool, not the regular Ethereum txpool.
EntryPoint
The singleton smart contract that orchestrates ERC-4337. Deploys per version on every supported chain at the same address (e.g., v0.6 at 0x5FF1...2789, v0.7 at 0x0000...a032). Runs the two-phase validate-then-execute lifecycle and settles gas fees to bundlers.
Bundler
An off-chain service that collects UserOperations from the alt-mempool, packs them into a single Ethereum transaction calling EntryPoint.handleOps, and earns the spread between user-paid priority fees and validator tips. Major bundlers in 2024-2025 include Pimlico, Stackup, Alchemy, Biconomy, and Candide.
Paymaster
A smart contract that volunteers to pay gas on behalf of a user in exchange for whatever consideration it chooses (nothing, an ERC-20 token, an off-chain sponsorship signature). Enables gasless transactions, pay-in-token UX (gas in USDC), and token-gated sponsorship.
Alt-mempool
The parallel mempool that ERC-4337 bundlers monitor. Distinct from the regular Ethereum txpool because UserOperations are not transactions at the protocol layer. Governed by ERC-7562 validation rules that prevent ops from interfering with each other.
validateUserOp
The function every ERC-4337 smart account must implement. Called by the EntryPoint during the validation phase to verify the signature, check the nonce, and (if no paymaster) pay the gas deposit. Bounded by ERC-7562 rules about which storage and contracts it may access.
validatePaymasterUserOp
The function a paymaster contract implements to decide whether to sponsor a given UserOperation. Returns a context blob for postOp settlement plus a validity window. The single chokepoint where paymaster business logic (sponsorship eligibility, token pricing) lives.
Aggregator
An optional ERC-4337 contract that combines many UserOperation signatures (typically BLS) into a single combined signature, verified once by the EntryPoint. Reduces gas dramatically when bundles are large; mainly relevant for high-volume L2s and gaming.
EntryPoint v0.7
The April 2024 EntryPoint release deployed at 0x0000000071727De22E5E9d8BAf0edAc6f37da032 on all supported chains. Introduced PackedUserOperation, separated paymaster address from paymaster data, and improved gas accounting. The dominant target for new ERC-4337 accounts in 2024-2025.

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