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 \texttt{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：以太坊区块构建者与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包后遵守拍卖结果。本文研究承诺问题。我们建模一个以概率$\varepsilon$违约的构建者，违约时会复制获胜MEV机会中特定类型$τ$的$γ(τ)$份额。搜索者预期这一行为，并在风险出价策略与安全威慑出价策略之间进行选择，后者使抢先交易无利可图。均衡态呈现分段特征：不完全承诺的成本取决于可复制性与竞争程度的联合效应。利用\texttt{libmev}数据集，我们从尾部贿赂平稳期估计$γ(τ)$，并将观测到的拍卖收入与违约构建者可捕获的盈余进行分解。结果显示不同MEV类型存在显著异质性：三明治机会已高度竞争，而裸套利和清算则使更多盈余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机制，还需对构建者事后利用观察到的出价和payload信息的能力施加约束。