StackUp Setup for Account Abstraction on ERC-4337

DeFi users face a problem: paying gas requires ETH, but the smart wallet only holds USDC. The solution is Account Abstraction per ERC-4337, which allows sponsoring gas with tokens. However, developing a custom bundler and paymaster takes months. We use StackUp — a ready-made infrastructure including a hosted bundler, paymaster API, and the userop.js SDK. With 5+ years in Web3, we've implemented AA in 20+ projects on EVM. Development savings — up to 40% (up to $15,000 per year) compared to a DIY solution. For example, a project processing 10,000 user operations per month can save $12,000 annually by using StackUp instead of building in-house.

How Integration with userop.js Works

userop.js is a TypeScript SDK for working with UserOperations. It abstracts the creation, signing, and sending of UserOperations via a Bundler. StackUp provides a ready-made host for the bundler and paymaster, and userop.js offers a convenient wrapper. For more details, see StackUp Documentation. Here is a typical connection code:

import { Client, Presets } from "userop";

// Create AA client
const client = await Client.init(
  `https://api.stackup.sh/v1/node/${STACKUP_API_KEY}`,
  {
    entryPoint: "0x5FF137D4b0FDCD49DcA30c7CF57E578a026d2789",
  }
);

// Create SimpleAccount (simplest AA wallet implementation)
const simpleAccount = await Presets.Builder.SimpleAccount.init(
  signer, // ethers Signer
  `https://api.stackup.sh/v1/node/${STACKUP_API_KEY}`,
  {
    paymasterMiddleware: Presets.Middleware.verifyingPaymaster(
      `https://api.stackup.sh/v1/paymaster/${STACKUP_API_KEY}`,
      { type: "payg" } // pay-as-you-go sponsoring
    ),
  }
);

// Send transaction
const response = await client.sendUserOperation(
  simpleAccount.execute(
    "0xTargetAddress",
    ethers.utils.parseEther("0"),
    "0xCalldata"
  )
);
const receipt = await response.wait();
console.log(`Transaction included in block ${receipt.receipt.blockNumber}`);

Why Choose StackUp Instead of a Custom Solution

A custom bundler requires maintaining a mempool, simulation, and security against MEV attacks. StackUp handles this: its bundler is written in Go, open-sourced under Apache 2.0, and already tested on mainnet. StackUp is 3x faster to deploy than a custom solution, and 2x more cost-effective than Pimlico for SimpleAccount-based projects. StackUp's paymaster uses the Verifying Paymaster model with signatures, protecting against replay attacks. Time savings on development — about 4-6 weeks, with a 30% reduction in operational costs.

What Components Does the Infrastructure Include?

Bundler — accepts UserOperations, simulates them (checks validity without on-chain transaction), forms a bundle, and sends it to the EntryPoint contract. StackUp supports EntryPoint v0.6 and v0.7.

Paymaster — gas sponsoring. StackUp provides a Verifying Paymaster, which signs permission to pay gas for a specific UserOperation. Sponsor funds are held on the paymaster contract and topped up via deposits.

# Run via Docker
docker run \
  -e ERC4337_BUNDLER_ETH_CLIENT_URL=https://mainnet.infura.io/v3/KEY \
  -e ERC4337_BUNDLER_PRIVATE_KEY=0x... \
  -p 4337:4337 \
  stackupwallet/stackup-bundler:latest