Ethereum's upcoming Glamsterdam upgrade introduces EIP-7732 enshrined Proposer--Builder Separation (ePBS), which improves the block production pipeline by addressing trust and scalability challenges. Yet it also creates a new liveness risk: builders gain a short-dated ``free'' option to prevent the execution payload they committed to from becoming canonical, without incurring an additional penalty. Exercising this option renders an empty block for the slot in question, thereby degrading network liveness. We present the first systematic study of the free option problem. Our theoretical results predict that option value and exercise probability grow with market volatility, the length of the option window, and the share of block value derived from external signals such as external market prices. The availability of a free option will lead to mispricing and LP losses. The problem would be exacerbated if Ethereum further scales and attracts more liquidity. Empirical estimates of values and exercise probabilities on historical blocks largely confirm our theoretical predictions. While the option is rarely profitable to exercise on average (0.82\% of blocks assuming an 8-second option time window), it becomes significant in volatile periods, reaching up to 6\% of blocks on high-volatility days -- precisely when users most require timely execution. Moreover, builders whose block value relies heavily on CEX-DEX arbitrage are more likely to exercise the option. We demonstrate that mitigation strategies -- shortening the option window or penalizing exercised options -- effectively reduce liveness risk.

翻译：以太坊即将推出的 Glamsterdam 升级引入了 EIP-7732 内嵌式提议者-构建者分离（ePBS），该机制通过应对信任与可扩展性挑战，改进了区块生产流程。然而，它也带来了一种新的活性风险：构建者获得了一种短期的“免费”期权，可以在不招致额外惩罚的情况下，阻止其已承诺的执行负载成为规范链的一部分。行使该期权将导致对应时隙产生空块，从而降低网络活性。本文首次对自由期权问题进行了系统性研究。我们的理论结果表明，期权价值与行权概率随市场波动率、期权窗口时长以及区块价值中源自外部信号（如外部市场价格）的份额增长而增加。免费期权的存在将导致定价偏差和流动性提供者损失。若以太坊进一步扩展并吸引更多流动性，该问题将加剧。对历史区块价值与行权概率的经验估计在很大程度上证实了我们的理论预测。尽管平均而言行权很少获利（假设 8 秒期权时间窗口下仅 0.82% 的区块），但在波动剧烈时期变得显著——在高波动日可达 6% 的区块，而这正是用户最需要及时执行的时候。此外，区块价值严重依赖中心化交易所-去中心化交易所套利的构建者更可能行使该期权。我们证明，缓解策略——缩短期权窗口或惩罚已行权期权——能有效降低活性风险。