Interpreting Ethereum Interoperability Layer (EIL): Bridging L2 Fragmentation and Building Seamless Cross-Chain Experiences

Author: Pan Zhixiong

Ethereum has successfully addressed scalability issues over the past few years by deploying multiple Layer 2 solutions such as Arbitrum, Optimism, Base, and others, resulting in reduced transaction costs and increased efficiency. However, a subsequent problem has emerged: fragmented user experience. Each L2 network functions like an isolated island, where users face cumbersome steps, different bridging protocols, and complex asset and gas management when cross-chain. To solve this pain point, the Ethereum core team recently proposed the Ethereum Interop Layer (EIL).

To understand EIL, we first need to review its foundation—ERC-4337.

ERC-4337 is an account abstraction standard proposed for Ethereum. It does not require any modifications to the underlying Ethereum protocol, but instead deploys smart contracts to realize a new type of account structure—smart accounts. These accounts support advanced features such as social recovery, multi-signature, batch operations, and more. They can also enable gas payments via ERC-20 tokens through smart contract mechanisms.

However, despite the technical innovations brought by ERC-4337, its widespread adoption in practice remains limited. Fragmented user experience, difficulties in multi-chain coordination, high gas costs, and ecosystem compatibility issues have all restricted the broad adoption of 4337.

EIL aims to address these problems based on ERC-4337. EIL is an additional multi-chain interoperability protocol layered on top of ERC-4337’s framework. It extends single-chain account abstraction to multi-chain account interoperability, enabling seamless experience across multiple L2 networks.

Specifically, EIL achieves two key innovations: Batch multi-chain operations with a single signature (batch authorization), and a bidding-based bridging liquidity provider (XLP) mechanism.

• The first innovation, batch authorization, allows users to authorize multiple operations across different L2 networks with a single signature. Implementation-wise, the wallet constructs individual UserOperations on each relevant chain, then combines these into a Merkle tree. The user only needs to sign the Merkle root once. When the smart account on each chain verifies the received UserOperation, it just needs to confirm that it belongs to the Merkle tree and that the signature is valid. This greatly simplifies cross-chain user operations.
• The second innovation, bidding-based bridging, introduces a role called Cross-chain Liquidity Provider (XLP). XLPs are responsible for transferring assets and paying gas fees across chains. When a user locks assets on the source chain and initiates a cross-chain request, multiple XLPs can compete via on-chain bidding. The winning XLP provides a cross-chain transfer voucher, which allows the user to directly receive funds and gas payments on the target chain to complete the operation. After the transaction, XLPs claim the assets previously locked by users on the source chain.

To ensure security and fairness, XLPs must stake collateral on the Ethereum mainnet (L1) and undergo strict dispute arbitration mechanisms. If an XLP violates the rules, its staked assets are forfeited, providing economic incentives to maintain integrity.

It’s important to note that EIL implementation does not require any modifications to Ethereum mainnet or L2 consensus protocols. All functions are built upon smart contracts and the existing ERC-4337 account abstraction framework. This design reduces implementation complexity and minimizes potential security risks to the underlying chains.

Of course, this design shifts some pressure and complexity to wallets and off-chain infrastructure. Wallets need to support complex multi-chain transaction construction, single-signature multi-chain validation, interactions with CrossChainPaymaster and XLP, and user-friendly interfaces. Off-chain infrastructure must establish robust bidding markets, monitor XLP fund flows in real-time, and manage risk.

Ultimately, EIL offers users an experience similar to a single chain. When users open a wallet supporting EIL in the future, they will no longer need to frequently switch chains, manage cross-chain assets, or endure long waiting times and cumbersome operations. All complex cross-chain details will be automatically handled behind the scenes, gradually unifying the user experience across the entire Ethereum L2 ecosystem, truly realizing the vision of multi-chain fusion and seamless interoperability.

EIL also opens a new realm of possibilities for the Ethereum ecosystem: it not only solves cross-chain user experience issues but, more importantly, ensures that multiple L2 networks can truly “integrate as one” in a secure, decentralized, and trust-minimized manner.