Ethereum, as a representative of Web3, adopts a novel framework called Proposer Builder Separation (PBS) to prevent the centralization of block profits in the hands of institutional Ethereum stakers. Introducing builders to generate blocks based on public transactions, PBS aims to ensure that block profits are distributed among all stakers. Through the auction among builders, only one will win the block in each slot. Ideally, the equilibrium strategy of builders under public information would lead them to bid all block profits. However, builders are now capable of extracting profits from private order flows. In this paper, we explore the effect of PBS with private order flows. Specifically, we propose the asymmetry auction model of MEV-Boost auction. Moreover, we conduct empirical study on Ethereum blocks from January 2023 to May 2024. Our analysis indicates that private order flows contribute to 54.59% of the block value, indicating that different builders will build blocks with different valuations. Interestingly, we find that builders with more private order flows (i.e., higher block valuations) are more likely to win the block, while retain larger proportion of profits. In return, such builders will further attract more private order flows, resulting in a monopolistic market gradually. Our findings reveal that PBS in current stage is unable to balance the profit distribution, which just transits the centralization of block profits from institutional stakers to the monopolistic builder.

翻译：以太坊作为Web3的代表，采用了一种名为提议者-构建者分离（PBS）的新型框架，以防止区块利润集中在机构化以太坊质押者手中。PBS通过引入构建者基于公开交易生成区块，旨在确保区块利润在所有质押者之间分配。通过构建者间的拍卖，每个时隙仅有一个构建者能赢得区块。在理想情况下，公开信息下构建者的均衡策略将促使其出价等于全部区块利润。然而，当前构建者已能够从私有订单流中提取利润。本文探讨了存在私有订单流的PBS机制效应。具体而言，我们提出了MEV-Boost拍卖的非对称拍卖模型，并对2023年1月至2024年5月期间的以太坊区块进行了实证研究。分析表明，私有订单流贡献了区块价值的54.59%，这意味着不同构建者对区块的估值存在差异。有趣的是，我们发现拥有更多私有订单流（即更高区块估值）的构建者更可能赢得区块，同时保留更大比例的利润。这类构建者进而会吸引更多私有订单流，逐步形成垄断市场。我们的研究揭示，当前阶段的PBS未能实现利润分配的均衡，仅仅将区块利润的集中对象从机构质押者转移至垄断性构建者。