Espresso is a coordination layer that facilitates interactions across blockchain ecosystems.
Chains looking to use Espresso integrate with:

1. The Espresso Network, a shared source of truth that provides fast finality on transaction ordering and data across chains

2. The Espresso Marketplace, which allows chains to sell transaction sequencing rights to block builders, maximizing chain revenue and minimizing friction in interoperating with other chains

Espresso is designed for any chain that is seeking efficient cross-chain coordination, sequencer decentralization, and/or seeking to increase the value it creates and captures.

Today, most of the chains integrating Espresso are Ethereum rollups, but any chain (including L1s) can work with Espresso.

Chains benefit from Espresso by being able to offer developers and users improved cross-chain experiences. Chains may also benefit from Espresso by increasing their chain's revenue.

Developers and end users who use chains that integrate Espresso also benefit through improved interoperability and composability relative to the existing fragmentation across chains.

Espresso is run by a network of node operators who participate in the consensus protocol (HotShot) and the data availability layer (EspressoDA).

While we have previously described Espresso as a “sequencer”, this is a little confusing and not quite accurate. Espresso does enable chains to share a sequencer, but is not a shared sequencer itself.

A “sequencer” is a term rollups use to describe the system component that proposes state updates (i.e., lists of transactions to be included in a particular order). In fact, in most L2s today, there is a permanent centralized sequencer that not only proposes but actually fully determines the list of transactions that define the L2 chain.

Espresso enables chains to sell the right to be the chain’s sequencer for a set amount of time to independent sequencers (which may be individuals or entities) bidding in the Espresso marketplace.

For centralized sequencers that is one and the same. There is one sequencing entity and that’s the protocol. It gets a bit more complicated for decentralized protocols.

We are referring to sequencers as the entities proposing the list of transactions. You may see other people and projects using “sequencer” to refer to the actor(s) with the ability to fully determine the transaction ordering of the rollup (as with L2s’ centralized sequencers today). In this case, this refers to the entire protocol since no single proposer will be able to provide full certainty around which transactions will be sequenced at any given time. But when you see Espresso talk about the “sequencer”, we mean the proposer.

“Shared sequencing” is enabled by the Espresso marketplace when two or more chains are assigned the same sequencer for a window of time. A sequencer can bid, via the Espresso marketplace, to build a block for a “bundle” of multiple chains at the same time. When a sequencer produces an ordered list of transactions for multiple chains at once, it can facilitate greater interoperability between the chains and satisfy user requests for cross-chain actions.

HotShot, Espresso’s proof-of-stake consensus protocol, allows the sequencer to offer the chains and their users a fast preconfirmation of the included transactions and their order.

Chains may also use Espresso without ever sharing a sequencer with other chains.

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That is one application of Espresso. However, even chains that choose to keep a fixed centralized sequencer can leverage Espresso’s fast finality layer, making it possible for end users and other ecosystem actors (e.g., bridge protocols and cross-chain liquidity providers) to very quickly confirm the most recent state of the rollup long before it is reflected and finalized on Ethereum. This facilitates faster bridging experiences.

Alternatively, a chain may choose to make the sequencer role distributed using Espresso’s marketplace. There are many reasons to do so, including (but not exclusively) decentralization.

Espresso offers a marketplace for chains to sell “sequencing rights” to bidders for a defined period of time (a timeslot). Sequencing rights refer to the right to propose which transactions, out of those that are submitted by users, are included, and their ordering.

There is a range and it is up to chains. For example this may include the rights to:

• Fully determine the transactions included and their order for a period of time (i.e., build blocks)
• Order a predetermined set of transactions or build blocks constrained by an inclusion list
• Control a fast lane of transactions that are prioritized by the rollup’s sequencer (e.g., in “Timeboost”)

Fully selling block building is the most straightforward and likely the most direct way to optimize chain revenue; however, there are tradeoffs and strong reasons to consider selling more restricted sequencing rights.

Sellers: Chains sell sequencing rights. Chains, in this case, generally refer to layer-2 or layer-3 rollups. However, layer-1 blockchains or even individual apps can also sell their sequencing rights.

Buyers: Sequencers. These are specialized actors who bid for transaction sequencing rights. For any given timeslot, the winning bidders are assigned to sequence transactions for their respective rollups. Sequencers may elect to further outsource the work of creating blocks to specialized “block builders” outside of the Espresso protocol, akin to the block builder ecosystem that has developed for Ethereum and various other layer-1 blockchains.

The Espresso marketplace is designed to increase a chain's potential revenue.

Today, L2s collect execution fees from users to cover execution costs and prevent spam. This is unchanged—these fees are still captured by chains directly within their execution environment (e.g., paid to the address of an operator, a DAO, etc).

Chains that participate in the Espresso marketplace may capture additional value from selling sequencing rights for more than they would make operating a sequencer on their own. This excess value may derive from user fees for fulfillment of various requests (including transaction priority or cross-chain dependencies); from arbitrage; or from cross-chain liquidity provision.

Some L2 sequencers today collect fees for transaction priority, but otherwise do not optimize block building or satisfy more complicated user requests in exchange for additional payment. Note that when a chain sells its sequencing rights in a timeslot it wouldn't collect those priority fees directly anymore, but in an efficient market it will receive at least that much (and likely more) from the sale.

Chains are free to set “reserve prices,” or the minimum amount for which its sequencing rights can be sold per timeslot. A chain may have a default sequencer that produces blocks for timeslots in which the sequencing right isn’t sold (because the reserve price isn’t reached).

All chains receive a distribution of the revenue for the bundle. This is done in a way that ensures the amount each chain in the bundle receives is greater than the amount it would receive if it weren’t included in the bundle (i.e., the higher value between its reserve price or the amount bid for this chain on its own).

Yes, actors that bid for sequencing rights pay a marketplace fee.

Marketplace fees discourage spam and cover operating costs.

A fee on surplus value transacted discourages "shill bidding"—when someone acting on behalf of the chain purposely submits an unrealistically high bid for the chain's sequencing right in order to claim disproportionate revenue from a rollup bundle.

This fee will be denominated in Espresso tokens and burned.

This is an active area of research and we will share more details soon.

Yes.

The token will, in conjunction with Ethereum restaking, act as a mechanism for proof-of-stake consensus in Espresso's HotShot protocol.

Bidders in the marketplace will also burn units of this token as a bidding fee. The token is not yet live.

Be very careful with what you read online. Any production launch of Espresso involving a token will only be announced, with ample advance notice, on official Espresso channels like our website and X/Farcaster accounts.

This depends on the chain. Some chains collect this value in a DAO treasury. Others have committed to using it for retroactive public goods funding and grants.

Some chains may also choose to redistribute revenue directly to users.

Yes.

Chains that are coordinating sequencing with other chains can still use Espresso and opt in or out at any time.

In addition to a sequencing marketplace, Espresso provides a means of finalizing proposed blocks and providing confirmations of this finality to users. This is sometimes called a finality gadget. The mechanism we use to achieve this is called HotShot.

HotShot is a proof-of-stake consensus protocol that is designed to be highly decentralized while also highly performant.

In the context of the Espresso marketplace, HotShot enforces the sale of sequencing rights to a given sequencer and ensures the entire network agrees on who is sequencing for each rollup bundle in each timeslot. It ensures that a current rollup sequencer's block proposal is quickly finalized and cannot be forked away. It also facilitates the smooth transfer of sequencing rights from one sequencer to another, ensuring that the next sequencer builds off the latest finalized rollup state.

HotShot also enables users and applications to obtain strong preconfirmations on the current state of each chain. This helps cross-chain liquidity providers and bridge protocols operate more efficiently.

Sequencers in the Espresso marketplace are required to broadcast their blocks to the HotShot network. They do not need to participate as a consensus node.

No, rollups can sequence their own blocks and have them notarized by HotShot consensus for fast finality and/or DA.

Yes, Espresso has a built-in data availability product that we also call Tiramisu (a reference to its three-layer architecture).

EspressoDA is unique in that it is designed with three layers, each with different security assumptions and performance properties, in order to optimize both resilience and performance.

Data availability is required for the Espresso network to function. As such, a lot of effort has been put into the design of the system to ensure it is low cost and highly performant.

Users of the Espresso network must use Espresso's data availability system. If these users would additionally like to use another data availability system, they can do so.

Espresso has released 5 testnets since 2022 and will be releasing its first production network in the coming months. We will be releasing more details on this and on our mainnet release soon.

Get in touch with us here and check out our documentation here.

We are currently conducting permissioned onboarding of node providers.

Ultimately, Espresso's mainnet will be fully permissionless and you will be able to start running Espresso nodes or participating as a sequencer in the marketplace by following our documentation. Our early docs for node operators can be found here. Feedback is welcome.

To get the benefits of Espresso as a user, you need to be using a chain or application that leverages Espresso. The chains that do so can be found here. If the app or chain that you use does not yet use Espresso, you should let them know by posting about it on Twitter or Farcaster and tagging Espresso. We are always welcoming more chains and applications to our growing ecosystem of projects who believe in a seamless, unified on-chain user experience.