Enshrined PBS (ePBS)

Enshrined Proposer-Builder Separation (ePBS) is a core protocol upgrade designed to formally and trustlessly separate the roles of block proposer (the validator selected to create a block) and block builder (the entity that assembles the block's transaction order and content). Unlike current off-chain implementations like MEV-Boost, which rely on external relay networks and introduce additional trust assumptions, ePBS aims to bake this separation directly into the blockchain's consensus rules. This enshrinement provides stronger security guarantees, reduces complexity, and ensures the separation is a native property of the protocol itself.

The primary motivation for ePBS is to manage Maximal Extractable Value (MEV) in a fair, transparent, and decentralized manner. By creating a dedicated market for block building, ePBS allows specialized builders to compete to create the most valuable blocks, with the winning builder's payload being committed to the chain by the selected proposer. This design aims to democratize access to MEV opportunities, prevent centralization risks associated with dominant builders or relays, and protect consensus validators from the operational and ethical complexities of optimizing block contents for profit.

A key technical challenge ePBS addresses is the two-slot proposal problem, ensuring the builder's block is published reliably without the proposer being able to steal or censor it. Proposed designs, such as those based on commit-reveal schemes or cryptographic commitments, involve the proposer committing to a builder's block header in one slot and then revealing the full block body in a subsequent slot. This mechanism, enforced by slashing conditions, makes it cryptographically costly for a proposer to deviate from the agreed-upon block, thereby securing the builder's work.

Implementing ePBS would represent a major evolution of Ethereum's consensus mechanism, following The Merge. It builds upon the foundational separation of execution and consensus clients by adding a formal economic layer for block construction. Successful enshrinement would likely render external proposer-builder separation middleware obsolete, simplifying the validator stack and creating a more robust and credibly neutral foundation for transaction ordering and MEV distribution across the network.

Enshrined Proposer-Builder Separation (ePBS) is a proposed upgrade to blockchain consensus protocols, most notably Ethereum, designed to formalize and secure the market for block production. It works by creating two distinct, protocol-defined roles: the proposer, who is responsible for including a block header and attesting to its validity, and the builder, who constructs the full block body containing transactions. The protocol enforces a commit-reveal scheme where builders submit encrypted block bodies and associated bids in a dedicated builder market, and the winning builder's payload is revealed only after the proposer commits to it. This separation is "enshrined" because the rules governing the interaction between proposers and builders are codified directly into the core protocol, unlike off-chain PBS arrangements which rely on trusted relay services.

The core workflow of ePBS involves a multi-phase block proposal process. First, during a bidding phase, builders compete by submitting cryptographically committed bids for the right to have their block included. The proposer then selects the header of the highest bid without seeing the block's contents, ensuring they cannot censor or manipulate transactions. After this commitment, the winning builder reveals their full block body. The protocol includes slashing conditions and crypto-economic incentives to penalize malicious actors, such as builders who fail to reveal a valid block or proposers who attempt to steal builder revenue. This design aims to maximize block value (MEV) for builders and proposers while minimizing trust assumptions and centralization risks inherent in off-chain relay models.

A key technical innovation in ePBS proposals is the use of a separate signature slot or a distinct builder channel. This architectural change allows the builder's contribution to be validated independently from the proposer's consensus duties. For example, a builder's block might be transmitted and attested to via a separate P2P subnetwork. This separation ensures that liveness and safety of the core consensus are not compromised by builder failure. Furthermore, by bringing the builder market on-chain, ePBS enhances transparency and auditability of the block production process, allowing anyone to verify the flow of payments and the execution of the auction rules directly on the blockchain.

The implementation of ePBS addresses critical limitations of the post-merge Ethereum ecosystem. Currently, proposer-builder separation (PBS) is implemented off-chain through a tripartite model of builders, relays, and validators. This introduces trust dependencies on relay operators to honestly mediate the auction and deliver blocks. Enshrined PBS eliminates this trusted third party by making the relay functionality a native protocol component. This reduces centralization vectors, mitigates censorship risks from relay policies, and creates a more robust and permissionless design. It represents a long-term evolution of Ethereum's roadmap towards a more efficient and credibly neutral block production market.

Enshrined Proposer-Builder Separation (ePBS) is a proposed protocol upgrade that moves the separation of block building and block proposing from an off-chain, social-layer market into the core Ethereum consensus rules. This architectural shift is primarily motivated by addressing systemic risks and inefficiencies inherent in the current, permissionless Proposer-Builder Separation (PBS) model that emerged from the MEV-Boost middleware. By enshrining these roles and their economic relationship in the protocol, ePBS aims to enhance censorship resistance, improve protocol simplicity and security, and ensure credible neutrality in block production.

The foremost motivation is strengthening censorship resistance. In the current PBS model via MEV-Boost, builders can filter transactions, potentially complying with external regulatory demands. While proposers can theoretically choose to bypass builders, the economic incentives to capture Maximal Extractable Value (MEV) are often overwhelming. ePBS designs, such as those requiring a proposer's commitment to a block header before seeing the full body, aim to cryptographically enforce that the highest-paying block is always included, making transaction censorship a protocol-level violation rather than a builder policy choice.

A second core motivation is protocol simplicity and security. The existing MEV-Boost ecosystem introduces significant complexity risk—it relies on trusted relay operators, requires additional software, and creates new attack vectors like relay outages or malicious payloads. Enshrining PBS simplifies the node operator's experience by baking the functionality directly into the client software, reduces reliance on extra-protocol actors, and allows for formal verification of the entire block production process. This moves critical economic activity from the fragile application layer to the robust, battle-tested consensus layer.

Finally, ePBS seeks to preserve Ethereum's credible neutrality and decentralization. The off-chain builder market risks centralization, as sophisticated builders with superior MEV extraction capabilities can outcompete others, potentially leading to oligopolistic control. By defining clear in-protocol rules for builder-proposer interaction and payment (e.g., via a commit-reveal scheme or a direct payment channel in the consensus protocol), ePBS can foster a more permissionless and competitive builder ecosystem, preventing the consolidation of block production power and ensuring the network remains resistant to capture.

Enshrined Proposer-Builder Separation (ePBS) is a core protocol upgrade designed to formally separate the roles of the block proposer (the validator selected to propose a block) and the block builder (a specialized entity that constructs the block's contents). This architectural shift, proposed for networks like Ethereum, moves the market for Maximal Extractable Value (MEV) from an off-chain, trust-dependent ecosystem into a transparent, cryptoeconomically secured protocol primitive. By enshrining these roles, ePBS aims to mitigate centralization risks in block building, reduce the trust assumptions required for proposer-builder coordination, and create a more equitable and verifiable distribution of MEV rewards.

The primary technical mechanism for ePBS involves a two-phase block proposal process. First, a builder network submits block bids—complete block headers with commitments to their contents and an attached bid—to the current proposer. The proposer then selects the header with the highest bid, signs it, and publishes it to the network, effectively committing to that builder's block without seeing its transactions. The builder subsequently reveals the full block body. This commit-reveal scheme ensures the proposer cannot steal the builder's work, while the builder's bond ensures they reveal the promised block. This design is a direct evolution of ideas pioneered by off-chain PBS implementations like mev-boost.

Implementing ePBS presents significant protocol design challenges, including managing builder censorship, handling builder failures where a block body is not revealed, and ensuring the system remains credibly neutral and resistant to manipulation. Proposals like Two-Slot PBS aim to address these by extending the consensus timeline across two slots, providing robustness guarantees. The transition to ePBS represents a major milestone in blockchain governance, as it would permanently alter the validator's economic role and require careful consensus-layer and execution-layer coordination, making its design and deployment a focal point of long-term ecosystem research and development.