Ethereum Proposer Builder Separation Explained
Estimated reading time: 4 minutes
- Ethereum’s Proposer-Builder Separation (PBS) launched in June 2025, reshaping block production roles.
- Block builders and block proposers are now distinct, enhancing transaction fairness and decentralization.
- PBS mitigates centralization and MEV extraction issues, fostering competition among block builders.
- The new system lowers the entry barriers for validators, making participation more accessible.
- Ethereum’s architecture is evolving, focusing on security and scalability improvements.
In June 2025, Ethereum launched its Proposer-Builder Separation (PBS) system, introducing a new structure for block production with significant effects on the network’s security, decentralization, and transaction marketplace.
PBS creates two distinct roles within the block production process: block builders and block proposers. Block builders are specialized groups that assemble candidate blocks using transaction fees, Maximal Extractable Value (MEV) opportunities, and compliance considerations as key factors[1]. They then submit these prepared blocks, along with incentive bids, to the proposers[1].
Block proposers—typically validators operating within Ethereum’s proof-of-stake protocol—select one of the submitted blocks for finalization. Their responsibility is to confirm the block and add it to the blockchain’s official record[1]. With PBS in place, validators are no longer required to handle the complexities of MEV extraction and instead focus on choosing the most beneficial block from those submitted by builders[1].
The development of PBS was largely prompted by concerns regarding transaction sequencing and network centralization. Previously, validators could influence the arrangement of transactions, which increased opportunities for MEV extraction and, in some cases, consolidation of power among resource-rich participants[2][3]. By separating the construction and finalization of blocks, PBS aims to distribute influence and reduce the potential for validator monopolies[2].
PBS also changes how MEV is distributed across the network. Instead of concentrating value in the hands of a single actor, the system splits extracted value between proposers and builders, introducing new incentives and encouraging competition[4]. While problems such as frontrunning persist, PBS has helped lessen their frequency and effects[4].
The introduction of PBS has led to the emergence of specialized block builder markets. In this environment, companies compete to optimize block value and propose better incentives to proposers[1]. This competitive dynamic encourages greater efficiency and stimulates new ideas around block construction and MEV reduction.
With PBS, validators do not need extensive knowledge of MEV extraction to participate. This change could lower entry barriers and make the validator role more accessible to smaller participants and those with fewer technical resources[1].
Deploying PBS required complex updates to the Ethereum protocol. Changes included defining responsibilities, building secure channels for builder-proposer communication, and refining the mechanisms that drive incentives within the new system[1]. These updates followed a period of research and testing, including transitional solutions such as MEV-Boost[1].
In the new structure, block builders assemble and validate transactions, while proposers review block metadata and confirm its validity before adding it to the chain[4]. PBS aims to strengthen both the security and scalability of the Ethereum network[5].
With the launch of Proposer-Builder Separation, Ethereum has redefined its approach to block production. The system seeks to address previous challenges related to centralization and MEV, while making the validator role more straightforward and accessible. Looking forward, PBS is positioned to influence both the network’s efficiency and its overall fairness.
- Nervos Knowledge Base, “What is Proposer-Builder Separation in Ethereum?”, https://www.nervos.org/knowledge-base/What_is_Proposer_Builder_Separation_in_Ethereum_(explainCKBot)
- Webopedia, “Proposer-Builder Separation (PBS) in Ethereum”, https://www.webopedia.com/crypto/learn/proposer-builder-separation-ethereum/
- Webopedia, “Proposer-Builder Separation (PBS) in Ethereum”, https://www.webopedia.com/crypto/learn/proposer-builder-separation-ethereum/
- Binance Academy, “Proposer-Builder Separation (PBS)”, https://academy.binance.com/en/glossary/proposer-builder-separation-pbs
- CoinBureau, “What is Ethereum? | Education”, https://coinbureau.com/education/what-is-ethereum/