Ethereum block builders run sealed auctions among searchers, but nothing in the protocol forces a builder to honor the auction outcome after observing submitted bundles. This paper studies the commitment problem. We model a builder who defects with probability $\varepsilon$ and, upon defection, replicates a type-specific fraction $γ(τ)$ of the winning MEV opportunity. Searchers anticipate this behavior and choose between a risky first-price bid and a safe deterrence bid that makes frontrunning unprofitable. The resulting equilibrium is piecewise, with the cost of imperfect commitment depending jointly on replicability and competition. Using the libMEV dataset, we estimate $γ(τ)$ from right-tail bribe plateaus and decompose observed auction revenue against the surplus a defecting builder could capture. The results show sharp heterogeneity across MEV types: sandwich opportunities are already highly competitive, while naked arbitrage and liquidations leave substantially more surplus exposed to builder defection. Credible MEV auctions, therefore, require not only an auction format, but also constraints on the builder's ability to use observed bid and payload information ex post.

翻译：以太坊区块构建者会在搜索者之间运行密封拍卖，但协议中没有任何机制强制构建者在观察到提交的捆绑交易后遵守拍卖结果。本文研究这一承诺问题。我们建模一个以概率 $\varepsilon$ 违约的构建者，违约时会复制获胜最大可提取价值机会中特定类型的 $\gamma(τ)$ 份额。搜索者预判此行为，在风险型第一价格出价与使抢先交易无利可图的威慑型安全出价之间做出选择。由此产生的均衡呈现分段特征，不完全承诺的成本同时取决于可复制性与竞争程度。利用libMEV数据集，我们从右尾贿赂平台估算 $\gamma(τ)$，并将观测到的拍卖收益与违约构建者可获取的剩余价值进行分解。结果表明不同MEV类型存在显著异质性：三明治机会已具高度竞争性，而裸套利与清算则让更多剩余价值暴露于构建者违约风险之下。因此，可信的MEV拍卖不仅需要合理的拍卖形式，更需要对构建者事后利用观测出价与负载信息的能力施加约束。