Introducing Espresso Confirmations

Underpinning Cross-Chain Composability

Composability is what separates building onchain from merely building online. It is the basis of the “infinite garden” — an open, permissionless environment where developers can build on existing smart contracts to create new products and experiences.

Building onchain has unleashed creativity and experimentation the restrictive APIs of Web2 and closed databases of traditional finance would never allow. We’ve escaped those walled gardens.

As onchain activity has taken off, the industry has innovated to meet that demand — scaling across many chains to support apps and their users. But today, these chains are siloes: competing for attention and fragmenting developers, users, and their capital.

At Espresso, we are in the business of empowering chains to deliver on their promise of open innovation. Our mission is to ensure that all chains work together as one unified system. An infinite garden has no walls.

Building together

Our mission to make chains composable is one shared across the industry. Rollup ecosystems are improving interoperability within their own clusters. Intents-based architectures introduce new ways to fulfill cross-chain user demands. Aggregated settlement systems and messaging protocols take aim at defragmenting liquidity and achieving even greater composability.

We are grateful to be tackling this problem alongside so many other projects and initiatives. The best way to achieve our vision will be together. Here’s how we at Espresso are contributing.

At Espresso, we divide our efforts into two categories:

• Espresso Product: building production-ready infrastructure that enables chains to coordinate and achieve composability with each other in an incentive-compatible way.
• Espresso Research: exploring the design space of cross-chain composability, developing proposals for potential new products, and testing ideas with collaborators.

The Espresso Network: a Global Confirmation Layer

We’re preparing to launch the Espresso Network on mainnet, marking our first production release and establishing the foundation for the future of cross-chain composability.

The Network underpins the range of Espresso Research proposals for products, protocols, and standards that will make all chains work together like a single, united system.

The Espresso Network is a Confirmation Layer that provides chain operators with information about the state of their own chain, as well as the states of other chains. These confirmations are important for cross-chain composability, which requires each chain’s full nodes to have access to reliable, credibly neutral confirmations of what’s happening on other chains in real time.

Espresso confirmations are more secure than centralized sequencer confirmations because they are backed by BFT consensus among a decentralized set of operators, and they are significantly faster than waiting for Ethereum L1 finality—occurring in a matter of a few seconds rather than 15 minutes. Moreover, Espresso confirmations will be backed by economic security as the network transitions to proof-of-stake.

When a chain integrates with the Espresso Network, its sequencer(s) publish blocks to Espresso, whose validators run BFT consensus to keep a consistent view of all published blocks. The chain’s L1 settlement contract only accepts blocks aligned with those published to Espresso, meaning anyone can confirm the chain’s state simply by reading and executing blocks on Espresso.

Key milestones along our journey have included:

• Shipping five testnets of the Espresso Network, including the most recent, Cappuccino, which finalized 3.7 million blocks over the course of four months.
• Developing frameworks to enable Arbitrum’s Nitro Stack, OP Stack, Polygon SDK, and others to integrate with the Espresso Network.
• Developing HotShot, our purpose-built BFT consensus protocol that prioritizes speed and scalability, making it a perfect complement to Ethereum’s consensus protocol, which prioritizes censorship resistance at the expense of speed.
• Securing integration plans with 16 rollups (and counting), as well as with bridges, solvers, and other market participants.

Why do we need a Confirmation Layer?

There are varying approaches to cross-chain composability. The Espresso Network and its confirmations play an integral role in improving or enabling them all. Examples include:

• More efficient intents-based bridging: The fastest way for users to bridge funds from one chain to another today is through third-party relayers/solvers, which underpin bridges like Across. It works like this: A user escrows funds on chain A, which the solver can recover only after paying the user on chain B (the destination chain). Today, most solvers risk getting rugged by sending the user funds on the destination chain without waiting for the user’s initial escrow transaction to settle. They do this to enable better UX, but adjust their fee to account for the risk. However, if chain A is integrated with Espresso, solvers can reliably confirm the escrow transaction within seconds. Moreover, the escrow contract cannot release funds to the solver before verifying a cross-chain message from the destination chain. With the Espresso Network this can happen faster, improving the capital efficiency of solvers.
• Faster, safer message-passing: Message-passing enables an application on one chain to read and trust an assertion about the state of another chain. Passing messages through Ethereum L1 is safe but slow (taking up to several days for optimistic rollups). Alternatively, apps can use trusted committees (like Wormhole, LayerZero, and Hyperlane), TEE attestations, or sufficiently fast ZK proofs to more quickly receive information about an external chain. But even honest committees who run full, executing nodes for the sending chain can’t confidently confirm the list of transactions sequenced until the L1 finalizes the transaction batches published by the chain’s sequencer (after 15 minutes). Similarly, apps would need a confirmed list of transactions (or Merkle root) to verify TEE attestations or ZK proofs against. Chains that integrate Espresso Network are prevented from altering their transactions once confirmed by Espresso, which takes only a few seconds, enabling faster and safer message-passing.
• Aggregated interoperability clusters: In an alternative design for messaging-passing, chains optimistically accept messages at low-latency from untrusted sequencers, and catch discrepancies at settlement time. This requires the chains to have a coordinated process for settlement, which can be based on ZK aggregation or an intertwined fraud proof mechanism. This pushes the problem of real-time message verification onto the rollup operators (who are incentivized to prevent a reorg) rather than being handled through the chain logic itself or through introducing new security assumptions. Rollup operators can leverage the Espresso Network for verifiable state proofs and fast BFT confirmations so that they have high confidence in the state of their rollup in real-time (as they generally do today instead of waiting for settlement time).
• Shared sequencers: Today chains typically have their own trusted sequencers they rely upon for fast confirmations. However, third-party sequencers can offer chains additional services, particularly around composability. For example, when a third-party sequencer operates for multiple chains at once it can promise users atomicity of their transactions across the different chains, even if those chains do not synchronously compose in a native way. However, it is difficult for chains to agree on a shared sequencer they trust for confirmations. The Espresso Network removes this problem by providing fast confirmations that do not need to come from the sequencer. Furthermore, if chains want to use a decentralized set of shared sequencers, or any kind of auction design that changes the sequencer frequently, a new sequencer can leverage Espresso Network confirmations to know which state to build upon when taking over from the last sequencer.
• Full synchronous composability: When aggregated interoperability clusters also use shared sequencers it is possible to achieve full synchronous composability. The Espresso Network plays a critical role for both of these components as detailed above.

Espresso Research: Exploring Composability in a Multi-Chain World

Proposing designs that achieve composability for chains, their developers, and their users—like those detailed above—has been central to our work on Espresso Research. For more on how we see the future getting built, you can find our research designs on HackMD or discussed in our research forum.

Two of our core Espresso Research initiatives include:

Cross-chain communication: We are proposing a stack-agnostic standard for coordinated and predictive messaging between chains, which we call CIRC (an acronym for Coordinated Inter-Rollup Communication). When coupled with the Espresso Network’s confirmations and an aggregated settlement solution (e.g., the AggLayer), CIRC will allow rollups to achieve full synchronous composability, regardless of VM, without sacrificing scalability or sovereignty, and even without needing to share a sequencer. You can read more on this design here.

Incentive-compatible shared sequencing: Shared sequencing is a powerful idea for cross-chain interactions, but suffers from challenges around incentive compatibility. In particular, rollups need a way to transparently split revenue when sharing a sequencer. To address this, Espresso Research proposes a marketplace enabling rollups to auction transaction-ordering rights to specialized block builders who will compete for opportunities to win batches of such rights for the rollups with the most cross-chain activity. The marketplace solves the social coordination problem of shared sequencing by introducing PBS to L2s, and providing a way for builders to efficiently bid on combinations of L2s instead of individually. With this market mechanism, L2s don’t sacrifice sequencer fees or sovereignty and enjoy better composability. To learn more about the Espresso Marketplace, read about our proposal here.

Looking Ahead

We’re excited to continue building the infrastructure to preserve the infinite garden: an ecosystem where all are welcome, apps seamlessly compose to create new experiences, and everyone can contribute. Join us in shaping this future — whether you’re building rollups, bridges, or are just an engaged community member.

Stay up-to-date as we prepare for mainnet by following us on X, joining our community on Discord, or contributing to our research forum.

Together we will safeguard the promise of an open, composable, unstoppable future for innovation.