Last updated November 7, 2023
ERC-4337 is a new Ethereum standard that enables account abstraction, allowing for gasless transactions, batched transactions, social logins, and more. As the ecosystem around ERC-4337 grows, several bundler packages have emerged, each with its own strengths and weaknesses.
Yes, we're mentioning ours first.
The Stackup bundler is a highly performant Golang bundler designed for easy integration with Go Ethereum (geth), and was the first production bundler on this list to be fully compliant with ERC-4337. It is actively maintained and has extensive documentation, making it the go-to option for most teams. Stackup offers access to hosted bundlers on their website, so you don't need to self-host a bundler. This is a great option if you want a high performance and battle-tested option with active support, or a hosted solution.
Stackup's bundler has been in production use since 2022, and boasts an over 99.9% uptime. It is also strictly compliant with ERC-4337, meaning that it is interoperable with any ERC-4337 service or application.
Written in typescript and developed by the original ERC-4337 authors, the ETH Infinitism reference bundler is a reliable and fully compliant option for developers. It was developed alongside the specification test suite also maintained by the ETH Infinitism team.
This is a great option if you prioritize compliance with the ERC-4337 specification over performance, or if you want to run a bundler locally and debug errors in a familiar Typescript format.
Rundler is a Rust bundler developed by Alchemy. This is a great option for users who are already Alchemy customers and need only basic ERC-4337 services. It has impressive uptime and complies with the ERC-4337 standard well. You may find some differences with some Alchemy-specific APIs, like their paymaster, but the Rundler itself is fully interoperable with other services.
Alto is a Typescript ERC-4337 bundler written by one of the co-authors of ERC-4337. As of November 2023 it is still in private beta, and is not fully ERC-4337 compliant. Interoperability with other bundlers may require additional effort, as Alto does not yet simulate transactions before including them on-chain. Pimlico's hosted bundler service is a good option if your application needs to support one of the blockchains that Pimlico supports but others do not.
Biconomy's bundler service is similar to Alto, in that it is a Typescript bundler that is not yet fully ERC-4337 compliant. It is a great option if you are building with Biconomy's SDK.
Vid Kersic, an ETH Protocol Fellow, is developing a Rust-based bundler for ERC-4337. This bundler is a great option for integration with other Rust tools.
Skandha is a Typescript bundler developed by Etherspot. Etherspot is actively involved in the development of the ERC-4337 bundler mempool specification. This is a great option if you are already leveraging Etherspot's SDKs for your application.
Developed by the Candide team for the Candide wallet, Voltaire is a Python implementation of the ERC-4337 bundler. This bundler is a great option if you are developing on top of Candide's open source wallet.
Each of these bundlers offers unique features and benefits, making it important for developers to carefully evaluate each option and choose the one that best fits their needs. As of February 2023 only two meet the ERC-4337 specification and pass the test suite: Stackup and ETH-Infinitism. The Stackup bundler is usually the best option of the five bundlers in development, but as the ERC-4337 ecosystem continues to grow we can expect to see more bundler options emerge, offering even greater flexibility and functionality to developers.