arXiv:2610.22451v1 Announce Type: new Abstract: Proof-of-Work blockchains increasingly rely on transaction fees to keep miners engaged as block subsidies decline. An immediate outcome of this is that miners may sit idle at the start of a round until enough high-fee transactions accumulate in order to make mining worthwhile. This idle period is known as the mining gap. We model the high-fee transaction backlog as a Lindley-type recursion under a two-tier fee market and use its stationary distribution to characterize the mining gap. Under Bitcoin's difficulty-adjustment mechanism, the expected gap grows strictly with the hashpower active on the network and consumes the entire round as that hashpower grows without bound. A free-entry condition determines a unique long-run equilibrium hashpower. Capital cost caps the equilibrium hashpower and prevents the mining gap from occupying the entire round. We further characterize how the block subsidy, transaction fees, and operating cost shape the equilibrium hashpower and the mining gap.