Our smart wallets and passkeys article covered what changes for you as a user when a wallet is a smart contract instead of a single private key. This one goes one level deeper, into the standard that makes it work: ERC-4337. If you have ever wondered how a transaction gets onto Base when there is no traditional private key signing it directly, this is the mechanism.
The problem ERC-4337 solves
Ethereum, and by extension Base, was originally built around one kind of account: an externally owned account, or EOA. An EOA is controlled by exactly one private key, and only that key can authorize a transaction. That model is simple and battle tested, but it is also rigid. An EOA cannot require a fingerprint instead of a signature, cannot let someone else pay its gas, and cannot bundle several actions into one approval, because the core protocol only understands "one key signs one transaction."
Changing that at the protocol level would mean a consensus upgrade across every Ethereum node, a slow and risky process. ERC-4337 took a different approach. Instead of changing the base protocol, it built a parallel system on top of it, using contracts that already exist today. The standard reached final status in March 2023 and has since been adopted across most EVM networks, including Base.
The three pieces
Three components work together to make an account abstraction transaction happen.
UserOperation. This replaces the idea of "a transaction" with "a signed intent." Instead of your wallet broadcasting a transaction the way an EOA does, a smart wallet builds a UserOperation, a data structure describing what it wants to do: which contract to call, what data to send, and how it authorizes the request, whether that is a passkey signature or something else entirely. A UserOperation is not a transaction yet. It is a request waiting to become one.
Bundlers. A bundler is a separate piece of infrastructure that watches for pending UserOperations, the same way a regular Ethereum node watches for pending transactions. When a bundler finds one worth including, it collects it, sometimes together with others, and wraps them into an actual transaction that it submits to the network using its own EOA. This is the detail that makes the whole system work without a protocol change: from the blockchain's point of view, the bundler is just a normal EOA sending a normal transaction. The complexity is hidden inside that transaction's data.
The EntryPoint contract. This is a single, shared smart contract that every bundler calls into. It receives the batch of UserOperations, checks each one against the smart wallet it claims to come from (does the signature check out, can the wallet cover its costs), and only then executes the requested action. Two versions of the EntryPoint have been in use, v0.6 from the 2023 launch and v0.7 from 2024, which added support for more flexible paymaster and validation logic. The EntryPoint is what gives smart wallets a common, audited gatekeeper instead of each wallet implementing its own untested version of this logic.
Put together, the flow looks like this: your smart wallet signs a UserOperation, a bundler picks it up and pays to include it in a real Base transaction, and the EntryPoint contract verifies and executes it against your wallet's own contract code.
Where paymasters fit in
The EntryPoint's validation step is also where gas sponsorship happens. Our gasless transactions article covers this from the user's side, but mechanically, a paymaster is a separate contract that the EntryPoint can ask "will you cover this UserOperation's cost instead of the sender?" If the paymaster agrees, under whatever rules its operator has set, the bundler gets reimbursed by the paymaster rather than by your wallet. Nothing about gas becomes free at the network level, the cost is simply redirected to whoever the paymaster's operator decided should pay.
Why this needs a smart contract wallet
None of this works for a plain EOA, because an EOA has no code and no way to define custom validation rules. It can only check one specific type of cryptographic signature, built into the protocol itself. A smart wallet, as described in our smart contract explainer, is a program, and that program is what defines what counts as a valid authorization for a UserOperation. That is why passkey support, gas sponsorship, and batched actions all trace back to the same root cause: the account itself is now code, not just a key.
Coinbase Smart Wallet, which works on Base, is built on this standard, and Base has consistently ranked among the more active networks for ERC-4337 activity since the standard matured.
What this means for you as a user
Almost none of this is something you need to manage directly. If you use a smart wallet, the UserOperation, bundler, and EntryPoint steps happen automatically between the moment you approve a passkey prompt and the moment your balance updates. What is worth understanding is what changed underneath: your approval no longer produces a signature that goes straight onto the chain. It produces a request that a separate piece of infrastructure, the bundler, has to pick up and pay to deliver. In practice this is reliable and fast on Base, but it is a genuinely different pipeline than the one an EOA uses, with more moving parts between your approval and final settlement.
The short version
ERC-4337 lets smart contract wallets send transactions without changing Ethereum's core protocol. Your wallet signs a UserOperation instead of a transaction, a bundler wraps it into a real transaction and submits it, and a shared EntryPoint contract checks it and carries it out, optionally with a paymaster covering the cost. It is the plumbing behind passkey logins, sponsored gas, and batched approvals on Base, and it is worth knowing about even though you will rarely, if ever, need to think about it directly.
If you would rather use a wallet built on the simpler, original EOA model, with a recovery phrase you fully control and nothing else in between, Simple Base Swap works exactly that way. Start at app.simplebaseswap.com.