Fidelity's Case for Bitcoin's Enduring Security: Why Attack Costs Always Exceed Honest Participation

Miners respond to total revenue, not just the subsidy. Gray argues that miner incentives encompass block rewards, transaction fees, and Bitcoin's market value together . As long as the total dollar value of those rewards justifies hardware and electricity costs, miners continue adding hash power—which raises the cost of mounting an attack .

The Mechanisms That Ensure Attack Costs Always Exceed Honest Participation

Fidelity's report goes beyond historical trends and lays out structural, game-theoretic reasons why attacking Bitcoin is economically irrational—now and in the future.

Self-fighting feedback loops during an attack. The report details how a 51% attack (whether censorship or double-spend) naturally triggers counter-incentives that mobilize honest participants without any coordination. For example, if an attacker produces empty blocks, users reprice transactions with higher fees, which incentivizes additional honest miners to bring hash rate online to compete directly with the attacker . Gray describes this as Bitcoin's incentive structure being "[re]active"—attack scenarios create market forces that pull hash power back to honest mining .

Censorship attack requires ~99% of hash rate to be sustainable. A censorship attack succeeds only if the attacker can maintain near-total control of block production. In practice, the rising fees that result from censored transactions attract competing miners, making it economically untenable for the attacker to hold that share for long .

Attack scope is inherently limited. Gray notes that even a majority of hash rate does not grant control over Bitcoin's ruleset—such as its maximum supply or issuance schedule. 51% attacks are therefore "limited in scope" and "inherently disruptive"—and have not been observed at scale to date .

The network is least attractive to attack when it is most vulnerable. Gray observes that in Bitcoin's early years, when hash rate was low enough that a 51% attack was technically possible, the network had negligible economic value, so there was no rational incentive to attack it . Conversely, once Bitcoin has substantial market value, the hash rate and energy expenditure securing it have already risen proportionally, making attack costs prohibitive .

No dependency on adoption or fee forecasts. The report deliberately avoids assumptions about future transaction fee levels or adoption rates. Instead, it examines attack viability directly, concluding that the economically rational response to any attack is to defend the network, not join the attacker .

The 0.195 BTC Subsidy Scenario (Circa 2040)

By standard halving projections, the block subsidy reaches ~0.195 BTC roughly five halvings after the April 2024 event—around 2040 (3.125 BTC → 1.5625 BTC → ~0.78 BTC → ~0.39 BTC → ~0.195 BTC) . Gray's argument applies generically to all future subsidy levels: the dollar value of the subsidy at any given epoch depends on Bitcoin's price at that time, and historically price appreciation has more than compensated for each 50% issuance cut . The report's core thesis is that security rests on the total value of all miner compensation (subsidy + fees) relative to energy costs, not on the subsidy's size in BTC, and that the network's self-correcting incentive mechanisms remain operative regardless of how low the subsidy falls .

Important Caveats

The analysis assumes persistent demand for Bitcoin. Fidelity acknowledges that if Bitcoin has no demand, most network dynamics become irrelevant—but in that scenario, the economic motivation to attack would also be near zero .

The report also notes near-term financial pressure on publicly traded miners, some of whom are diversifying into AI/HPC operations. But Gray distinguishes miner corporate stress from Bitcoin's base-layer security, which he argues remains intact .