How Across uses modularity to enable cross-chain interoperability

Tldr; Across is the first system that uses a modular, intents-based architecture to enable cross-chain interoperability. Modularity is key to its design, putting Across at the forefront of interop innovation and unlocking new possibilities for applications and users in a secure manner.

Key takeaways:

• Across is a modular, intents-based system that allows applications to access capital and fulfill cross-chain intents for users.
• In defining its tech stack as individual modules, Across gives applications a way to plug into the features they need to offer interop services.
• The system’s modular design connects users to applications, while its intents-based framework offers significant UX benefits.
• Modularity turns Across into a fully-fledged cross-chain interoperability solution, representing an evolution from the protocol’s early bridge product.

When Across launched in late 2021, it had a simple goal: to help users securely move assets between chains at a high speed and low cost. The solution quickly found success because it was extremely effective at this objective thanks to its intents-based design.

Across recently unveiled its V3 upgrade, which defines each layer of the system’s stack as individual modules. This upgrade makes Across Web3’s first cross-chain intents execution system with a modular-based architecture. The system’s modular design has profound implications for applications and users, evolving Across into a fully-fledged cross-chain interoperability platform.

In this deep dive, we explain Across’ modular architecture and why it marks a breakthrough in interop, the benefits of intents, and how we see these designs impacting the cross-chain landscape in the long-term future.

Unpacking Across’ modular framework

To start off, it’s worth defining what we mean when we talk about “modularity.” This term refers to a system’s ability to be partitioned into individual components or modules. Modularity has recently caught on in Web3 as a way of categorizing “modular” and “monolithic” blockchains. Modular blockchains like Ethereum and Cosmos are composed of multiple layers that fulfill different functions, while monolithic blockchains like Solana handle everything through a single layer.

Modularity makes Across a fully-fledged cross-chain interoperability platform.

Across is a modular, intents-based system. This system can be unbundled into three layers: intent, relayer, and settlement.

The intent, relayer, and settlement layer.

The intent layer — this is where the user goes to express their intent. That might be a simple $USDC transfer from mainnet to L2 or it might be a request for an action like a swap for $ETH at the destination. The intent layer is there to let the user articulate what they want to happen after they make a deposit at the origin.

The relayer layer — when a user expresses their intent, relayers (otherwise known as fillers or solvers) compete to fill their order at the relayer layer. Relayers must front their own capital to do this, and as they’re competing with one another, the user gets their order filled at a high speed and low cost.

The settlement layer — at the settlement layer, the user’s order is settled once the relayer gets repaid. In Across Settlement, the relayer fulfills the user’s intent and gets repaid in bundles, which saves gas. Across optimistically verifies repayments with UMA’s Optimistic Oracle, minimizing onchain actions and reducing costs. Across’ settlement layer settles any intents-driven order flow, allowing applications to offer cross-chain actions.

These layers can be thought of as modules within the system’s stack. Each layer has a distinct function and together they form a complete cross-chain interoperability solution.

Modularized cross-chain interoperability

Within each layer, there are crucial components that help the system offer best-in-class cross-chain execution. The intent layer prioritizes simplicity, where the user only needs to make a deposit and express their desired outcome. Today, users make a deposit at the origin with the Across Bridge, but in the future they could sign a gasless order. The system’s intents-based architecture enables this seamless, low-cost user experience. The relayer layer works because a network of third-party relayers races to fulfill user intents as quickly as possible at an attractive price. At the settlement layer, relayers are repaid in bundles for fronting their capital. They are repaid promptly using LP capital deposited into a pool on mainnet, with the pool rebalanced through each chain’s canonical bridge. The OO is also important here because it settles disputed repayments.

From the relayer network fulfilling intents through to the third-party LPs and OO enabling and validating repayments, each component helps the system offer seamless cross-chain interoperability in a trustless manner.

Why Across uses an intents-based framework

Across adopts an intents-based framework where the user expresses their desired outcome and relayers compete to fulfill their intent.

While intents are not the only way to transfer assets between chains, other approaches pose significant security risks. Lock-and-mint bridges create honeypots for hackers and messaging (otherwise known as delivery-vs-payment) systems can be gas-intensive.

There is a trade-off to using intents. But the user is not burdened with the risk when they express their desired action because the relayer carries the cost. The relayer takes on finality risk (as they can front their capital before the user’s deposit is finalized) and the risk of being repaid (meaning they must trust UMA to validate their repayment).

Relayers get repaid at the settlement layer when they fulfill user intents.

There are notable benefits to this: the user gets their order filled fast and the relayer’s repayment can happen separately with less urgency. In turn, this saves costs and maximizes security with optimistic bundled repayments.

Across’ intents-based design makes it the quickest and cheapest way for users to transfer assets between chains. With the system’s modular architecture, applications can use intents to offer their users an abundance of cross-chain possibilities.

The system’s modular architecture makes seamless cross-chain execution available to applications and users, while the intents-based design ensures users get a good experience when they make their request.

How applications can plug into Across

As Across is unbundled in modules, applications can plug into the system’s layers to cater to their users.

At the intent layer, applications can submit intent order flow. The Across Bridge is an example of a source where users express an intent but other designs can use the relayer layer to make a submission to Across’ system.

At the relayer layer, applications can access a competitive network of relayers, where the relayers respond to order flow from the intents layer. Across has a robust relayer network today but could use standardization to make it more accessible to more relayers in the future (and relayers could fill orders from multiple sources).

At the settlement layer, Across settles cross-chain intents for applications with the best capital efficiency and speed. Relayers get a good service because they receive gas-efficient optimistic bundled repayments and they can join a robust network. In turn, they have lower costs and the user gets a better experience. Across can settle orders for any application that generates intent order flow even if the order flow does not originate from Across’ intents layer. In other words, Across can settle any source of intent order flow in the most capital efficient manner.

The individual modules in Across’ tech stack form one cross-chain interoperability system. Across offers users and applications three products:

Across Bridge — extremely high-speed, low-cost bridging, integrating each of the system’s three layers.

Across+ — bridge abstraction with cross-chain hooks, where bridging and protocol actions are bundled and the user expresses their desired action with a single signature.

Across Settlement — the first production-ready, modular settlement layer for settling cross-chain intents, offering capital-efficient settlement for any application that originates intent order flow.

In summary, Across is a first-of-its-kind, modular system, where any application can plug into individual modules for their own needs and the system can settle any intent order flow.

The endgame for modular interoperability

Across became a dominant solution in the cross-chain space because it offered users a good experience for transferring assets between chains. This is a goal most traditional bridges aspire to — they literally act as a “bridge” from one blockchain to another and they want to serve users quickly and cheaply.

Across’ modular-based design elevates the solution so that users are connected to applications. The end goal is not just facilitating blockchain to blockchain transfers — applications now have better access to users and users can now commit any kind of action across the ecosystem.

Modularity is the endgame for cross-chain interoperability and Across is blazing the trail.

The first version of Across optimized for capital efficiency and user experience. With the latest upgrade, Across gives users more options with the superb UX they’re accustomed to. Across V3 was designed around the thesis that users really want to use applications, not blockchains. You don’t just transfer $ETH to Base to leave it sitting there; you do it because you want to play with an application.

Modularity is key to Across’ design. It exposes the entire stack to applications and users, giving them more choices with cross-chain intents. It’s our view that modularity is the endgame for cross-chain interoperability and Across is blazing the trail to serve users.

Across and the future of interop

Across is not just a solution for transferring assets quickly, cheaply, and securely. It does this extremely well, but in defining the system’s individual modules, it can offer seamless cross-chain interoperability to a much wider user base.

Thanks to its modular design, we can think of Across as a developer tooling protocol for interop solutions to plug into. Any application can use Across’ intents-based architecture to fulfill user needs — in a sense, applications are now Across users. Across is the first Web3 application to settle cross-chain intents.

Modularity creates new possibilities for cross-chain explorers, expanding the concept of “bridging” as we know it. This is the future of interop — and Across is already leading the way.

References

• Across V3: Introducing the First Intents-Based Interoperability Protocol [Across]
• Axelar Docs [Axelar]
• Hyperlane Docs [Hyperlane]
• Permissionless Interop for The Upcoming Modular Expansion [The Rollup]
• Synapse Docs [Synapse]
• The case for canonical asset bridging: Why are bridge hacks so common? [@dreamsofdefi for Across]
• The intents bridge: Cross-chain value transfer and the future of interoperability [@dreamsofdefi for Across]
• The intents bridge: How Across uses optimistic verification to lower costs [@dreamsofdefi for Across]
• What is xERC20? [xERC20]
• What are xERC20 tokens? [Connext]
• Why Intents are the Answer to Interoperability [Across]
• Why Is Financial Engineering Important in Bridging? Episode 1 [@kevin-uma for Across]