Set up the ERC-4337 environment
Before building the gas sponsorship logic, you need a working ERC-4337 environment. This section covers installing the core SDKs and connecting to a testnet provider so your AI agent can interact with the bundler and paymaster contracts.
Start by installing the official Paymaster Kit package. This SDK provides the utilities for creating, signing, and submitting user operations. Run the following command in your project directory:
Next, connect to a bundler node. The bundler aggregates user operations and submits them to the mempool. For testing, use a public testnet bundler like the one provided by Alchemy or a local instance.
Initialize the provider in your code:
Test the connection by fetching the gas price from the bundler. This step confirms that your environment is correctly configured and ready for gas sponsorship logic.
Configure gas sponsorship logic
The core of any AI agent gas sponsorship system is the paymaster contract, which sits between the user’s smart account and the bundler. Under ERC-4337, the paymaster must validate the transaction and provide the signature that covers the gas costs. For AI agents, this logic isn’t just about validation; it’s about financial control. You need to decide how the agent pays for execution: does it cover a fixed amount of gas, or does it take a percentage of the transaction value?
Choosing the right sponsorship model determines how your agent behaves under load. A fixed cap offers predictable costs but risks failing if gas prices spike. A variable percentage model scales with the transaction but requires careful handling of ERC-20 approvals and slippage. Below is the step-by-step process for implementing these two primary logic paths.
The fixed cap model is the simplest form of sponsorship. The paymaster contract specifies a maximum amount of gas units (or wei) it is willing to pay for a single transaction. If the actual execution cost exceeds this cap, the transaction reverts. This is ideal for AI agents performing routine, low-complexity tasks like data fetching or simple state updates. In your contract, define a constant MAX_GAS_LIMIT and check the preVerificationGas and gasFees during the validatePaymasterUserOp function. If the sum exceeds the limit, revert the operation. This prevents runaway costs during network congestion.
For AI agents executing trades or complex DeFi interactions, a fixed cap is often insufficient. Instead, implement a percentage-based sponsorship. The paymaster calculates the gas cost as a percentage of the transaction’s value or the ERC-20 token amount being transferred. To do this, you must extract the token transfer details from the user’s callData and apply your sponsorship rate (e.g., 0.5% of the gas cost). This model aligns the sponsor’s cost with the user’s benefit, but it requires robust parsing of the callData to accurately determine the transaction value before signing.
Regardless of the model, you must implement hard caps to protect the AI agent’s treasury. Unlimited gas sponsorship is a critical vulnerability; a compromised agent key could drain funds through high-frequency, high-gas transactions. Set a daily or session-based spending limit in your paymaster state. Additionally, verify that the beneficiary address (the one receiving the gas refund or payment) is authorized. If using ERC-20 tokens for gas, ensure the user has approved the paymaster contract for the necessary amount before the transaction is submitted to the bundler.
Once your logic is in place, test it against the entry point contract. Use a local testnet environment with a bundler like Alchemy or Stackup to simulate user operations. Verify that the paymaster correctly signs valid transactions and reverts those that exceed your defined limits. This ensures your AI agent can operate autonomously without manual gas interventions.
Link AI Agent Wallets to the Paymaster
To enable gasless transactions for AI agents, you must connect your AI agent's Smart Account to the Paymaster contract. This integration allows the agent to execute complex workflows—such as executing trades, minting NFTs, or interacting with DeFi protocols—without holding native ETH or the chain's native token for gas fees. The Paymaster acts as the sponsor, covering the gas costs in exchange for a fee paid in ERC-20 tokens or absorbed by the protocol.
The core mechanism relies on ERC-4337 (Account Abstraction). Unlike standard EOAs (Externally Owned Accounts), Smart Accounts can validate and pay for gas within the same transaction context. By implementing the IAccountPaymaster interface, you grant the Paymaster the authority to verify the agent's intent and release funds to the Bundler only when the transaction meets your specific criteria.
Configure the Smart Account
First, ensure your AI agent is initialized with a Smart Account implementation, such as SafeCore or Account Kit. These accounts come with pre-installed entry points that allow them to interact with the Paymaster. You do not need to build the wallet from scratch; instead, focus on configuring the account to recognize your Paymaster's address as a valid sponsor for specific operations.
Implement the Paymaster Logic
Your Paymaster contract must implement the preOp and postOp hooks. In the preOp phase, the Paymaster validates the agent's request. For AI agents, this is where you add custom logic to prevent abuse—for example, checking if the agent's signature is valid or if the requested operation falls within its allowed scope. If the validation passes, the Paymaster deposits the required gas fee into the Entry Point contract.
Connect via the Bundler
The AI agent does not pay gas directly. Instead, it sends the signed transaction bundle to a Bundler. The Bundler forwards this bundle to the Entry Point, which then calls your Paymaster's preOp method. If the Paymaster approves, the Bundler includes the transaction in a block. The Paymaster then reimburses the Bundler (or the fee is deducted from a prepaid balance) via the postOp hook. This flow ensures the agent remains gas-free while the system maintains security and cost control.
Test the Integration
Before deploying to mainnet, simulate the agent's transaction flow using a testnet. Use tools like Alchemy's Paymaster SDK or SafeCore's operations kit to verify that the Paymaster correctly validates the agent's signature and covers the gas costs. Monitor the transaction status to ensure the Bundler relays the transaction successfully and the Paymaster's balance updates as expected.
Test the paymaster kit 2026 deployment
Before exposing the AI agent gas sponsorship to mainnet traffic, you must verify that the ERC-4337 paymaster contract correctly handles validation, execution, and funding edge cases. A robust test suite ensures that the agent can trigger transactions without user wallet balance, even when the paymaster's ETH balance fluctuates or signatures expire.
Deploy your ERC-4337 bundler locally (e.g., using Foundry or Hardhat) and configure the paymaster to accept the specific EntryPoint version. Execute a batch of transactions initiated by the AI agent's smart account. Verify that the simulateValidation call succeeds and that the bundler accepts the entry point without reverting.
Test the paymaster's validatePaymasterUserOp method with both valid and invalid signatures. Ensure that the contract correctly parses the context data provided by the bundler. Check edge cases where the signature is malformed or the user's account has not yet been initialized, confirming that the paymaster rejects invalid ops with the correct error strings (e.g., "AA25 invalid account nonce" or "AA24 expired or not due").
Simulate a scenario where the transaction gas usage exceeds the initial estimate. Confirm that the paymaster correctly calculates the preOpGas and postOpGas to ensure the user's account (or the paymaster itself) is not overcharged. Test the refund logic by sending a transaction that uses less gas than the gasLimit specified, ensuring the excess is returned to the sponsoring entity.
Drain the paymaster's ETH balance to zero and attempt to sponsor a new transaction. Verify that the contract reverts with a clear "insufficient funds" error rather than hanging or causing a bundler timeout. This ensures the AI agent's monitoring system can detect the funding issue and trigger a refill mechanism before user experience is impacted.
Common questions about ERC-4337 paymasters
When integrating a Paymaster Kit 2026, developers often encounter specific friction points regarding gas sponsorship mechanics and ERC-4337 compliance. These answers clarify how the paymaster interacts with smart accounts and AI agents to ensure seamless transaction execution.
These questions highlight why ERC-4337 is the preferred standard for modern crypto applications. By offloading gas management to a paymaster, you enable smoother interactions for both human users and autonomous AI agents.
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