From MEV-Boost to BuilderNet: Can True MEV Fairness Be Achieved?

Author: 0XNATALIE

Centralization in Ethereum Block Building

Currently, the Ethereum block building market faces a high degree of centralization, with approximately 92% of Ethereum blocks built via MEV-Boost, and around 94% of these blocks dominated by just two major block builders—Beaverbuild and Titan.

Flashbots introduced MEV-Boost to mitigate the economies of scale that large staking pools have in extracting MEV, preventing large validators from leveraging higher MEV revenues to strengthen their competitive advantage, which could force smaller validators into larger staking pools and further centralize the network. MEV-Boost implements Proposer-Builder Separation (PBS), decoupling the block proposing and block building processes. Block proposers (validators) are responsible for proposing new blocks, while block builders handle transaction ordering and block construction. This way, validators no longer directly engage in block building but instead rely on independent builders, redistributing MEV and reducing monopolization by large staking pools.

However, as MEV-Boost gained popularity, the block building market itself became highly centralized, with over 90% of blocks produced by only two builders. This concentration not only undermines Ethereum’s decentralization but also creates a vicious cycle of high participation costs, evident in two key aspects: First, order flow—the value of a block is determined by its order flow. To access this transaction data, builders must sign exclusive agreements with order flow providers (such as users, wallets, and applications), often involving high fees. Without paying these fees, builders struggle to compete. These exclusive arrangements allow a few builders to form monopolies with specific order flow providers, increasing systemic fragility—any single builder’s failure could impact overall network stability. Second, block building requires significant capital investment in infrastructure (e.g., relays), further raising the barrier to entry.

BuilderNet: Reshaping the MEV Ecosystem

To address these issues, Flashbots, Beaverbuild, and Nethermind have jointly developed BuilderNet, a decentralized block building network. By leveraging Trusted Execution Environments (TEE) and multiple independent nodes collaborating to build blocks, BuilderNet enhances Ethereum's censorship resistance, decentralization, and transparency, while redistributing MEV to ensure all participants benefit fairly.

Core Team

• Flashbots: A technical team focused on optimizing Ethereum MEV, committed to improving transparency and decentralization in the block building market. Flashbots developed protocols such as MEV-Boost and MEV-Share, providing more transparent and fair mechanisms for the block building ecosystem.

• Beaverbuild: A leading Ethereum block builder and one of the largest in the market, currently holding about 50% market share.

• Nethermind: A company providing Ethereum clients and infrastructure solutions, specializing in protocol implementation, performance optimization, and security. Nethermind delivers critical technical support for BuilderNet, ensuring efficient and secure system operations.

How It Works: TEE + Order Flow Sharing = Reward Distribution Based on Contribution

BuilderNet relies on a decentralized, multi-party collaboration model. In the traditional model, a single node runs one block builder; in the BuilderNet model, multiple nodes jointly operate a single block builder.

Within a block builder, each node runs an independent block building instance inside its own TEE. A TEE is a hardware-level secure environment that ensures transaction data privacy, prevents operators from tampering with transaction flows or leaking user data, and allows only authorized participants to verify and send encrypted transaction flows to these TEE instances. This mechanism guarantees both data privacy and system security. Each instance retrieves order flow from the entire network and independently constructs a complete block, while simultaneously sharing its order flow with other instances within the same builder. All resulting blocks are then submitted to the MEV-Boost relay, where a bidding mechanism selects which block will be included on-chain. The winning block’s revenue is distributed as refunds based on the contribution of each participant—such as applications, wallets, searchers, and instances—that provided order flow to that block.

BuilderNet supports not only the Ethereum mainnet but also plans to extend functionality to L2 networks through Rollup-Boost. In the long term, as more users adopt BuilderNet, even large builders will be incentivized to join the platform. Greater transaction volume and more efficient operations will enable them to achieve more stable returns.

Participants

• Users, wallets, and applications: Can participate by sending transactions to BuilderNet nodes and receive refunds based on their contribution.

• Searchers: Can submit transaction bundles to BuilderNet, enjoying privacy protection and earning refunds. This provides independent searchers with the same economic rewards and privacy protections as integrated searcher-builder entities.

• Builders (nodes): Independently run block building instances, submit blocks to MEV-Boost, and receive corresponding rewards based on their contribution.

• Validators: During the initial phase of BuilderNet’s launch, there will be no significant impact on validators’ economic model, as existing MEV revenues are typically not paid directly to them. However, more MEV will be redistributed to validators in the future.

• Operators: Responsible for managing and maintaining the infrastructure of BuilderNet nodes and ensuring the proper operation of TEE environments.