Bitcoin's block reward is scheduled to decline to zero, raising concerns about whether the network can remain secure once miners rely solely on transaction fees. This paper seeks to identify the conditions under which large-scale and persistent deviation from honest mining can arise. We analyze and compare the payoffs of honest and deviating miners in a sequential decision model, and identify a deviation threshold $G_t$ at which honest mining ceases to be privately optimal. Around the 2024 Bitcoin halving, we show that current mining behavior does not exhibit large-scale or structural deviation. However, when the block reward is removed, the $G_t$ criterion implies that deviation can arise even with a very small fraction of transaction fees. Finally, we evaluate three protocol-level mechanisms: Base Fee, Fee Floor, and an adaptive maximum block size rule, and show that their combination raises the deviation threshold and mitigates incentive breakdown in a fee-only regime. These results provide a practical benchmark for assessing Bitcoin's security as block rewards disappear.

翻译：比特币的区块奖励计划逐步降至为零，这引发了对网络安全的担忧：一旦矿工仅依赖交易手续费，网络能否保持安全？本文旨在识别大规模、持续性偏离诚实挖矿行为的条件。我们通过序贯决策模型分析并比较诚实矿工与偏离矿工的收益，发现当诚实挖矿不再具备私人最优性时存在一个偏离阈值 $G_t$。基于2024年比特币减半前后的数据，我们证明当前挖矿行为并未表现出大规模或结构性偏离。然而，当区块奖励完全消失时，$G_t$ 准则表明即使交易手续费占比极低，偏离行为也可能出现。最后，我们评估了三种协议级机制：基础费用、手续费下限及自适应最大区块大小规则，并证明它们的组合能提高偏离阈值，在仅依赖手续费的制度下缓解激励失效问题。这些结果为评估区块奖励消失后比特币的安全性提供了实用基准。