Bitcoin's Security Budget:
What Happens When Rewards Run Out?

What Is Bitcoin's Security Budget?

Bitcoin's security comes from proof of work. Miners spend real money on hardware and electricity to compete for block rewards. That competition creates a moat: to attack Bitcoin, you need to outpace all honest miners combined, which requires an enormous, ongoing expenditure.

The "security budget" is simply the total revenue miners collect per block. Today it has two components: the block subsidy (currently 3.125 BTC, worth roughly $220,000 to $260,000 at mid-2026 prices) and transaction fees (typically $3,000 to $15,000 per block depending on congestion). Together they determine how much miners can afford to spend on hardware and power.

The concern is straightforward. Bitcoin's code halves the block subsidy every 210,000 blocks, roughly every four years. Here is the schedule:

Each halving cuts the subsidy in half. Fees need to grow proportionally to keep total miner revenue constant. If they do not, the security budget falls and the cost of attacking Bitcoin falls with it.

Why This Is a Legitimate Concern

Transaction fees today cover roughly 2% to 8% of total miner revenue. The 2024 halving cut the subsidy from 6.25 BTC to 3.125 BTC. Fee revenue did not double to compensate. The next halving in 2028 will cut it again.

Researchers have modeled the consequences. A 2016 Princeton study identified what it called the "stability problem": without sufficient fee revenue, miners could have short-term incentives to fork the chain rather than extend it, since a fork allows double-spending the fees from the most recent block. The University of Luxembourg published similar analysis. Duke researchers examined how selfish mining strategies become more attractive as subsidies shrink.

None of these papers argue that Bitcoin will definitely fail. They argue that a fee-only security model has never been tested at scale, and that the current fee market may not naturally generate enough revenue without deliberate effort. That is a meaningful distinction.

Bitcoin optimists counter that rising BTC prices compensate for falling subsidy quantities, that Lightning Network growth drives more on-chain settlement, and that high-value applications will create natural demand for block space. These arguments have merit. The honest position is that no one knows which view is correct, and the stakes are high enough that the question deserves serious attention.

How Fee Revenue Has Behaved

Bitcoin's fee market is volatile. Block space is a fixed resource: each block can hold roughly 1 to 4 MB of transaction data. When demand for block space is high, fees spike. When demand is low, fees drop nearly to zero.

The 2024 halving block itself was a notable outlier: the rarity of the event created enormous competition for inclusion, pushing fees to record levels. Ordinals and Runes created genuine sustained demand for block space in 2023 and 2024. These events show that fee spikes are possible. What remains unclear is whether consistent, everyday demand will grow enough to replace subsidy revenue on a structural basis.

For context: to replace a 3.125 BTC block reward at $85,000 per BTC with fees alone, the network would need roughly $265,000 in fees per block, consistently. That would require sustained fee rates of around 150 to 200 sat/vByte on a fully congested network. Possible during bull markets. Not guaranteed over a decade.

Approaches Being Explored

Several directions exist for sustaining miner revenue as subsidies decline. They are not mutually exclusive, and the most likely outcome is some combination.

None of these approaches is proven at the scale needed. The halving schedule gives roughly a century to find answers, but the urgency increases with each halving as the subsidy shrinks faster in absolute terms.

NAT Specifically: What It Is and What to Make of It

NAT (ticker: $NAT, full name DMT-NAT) launched in November 2023. It uses the TAP Protocol, a meta-protocol built on Bitcoin by the German company Trac Systems. The core mechanism is unusual: every Bitcoin block contains a field called bits, which encodes the current mining difficulty target. TAP Protocol reads this field and generates approximately 386 million NAT tokens per block. These go to the miner who found the block.

The bits field is required for consensus. Unlike Ordinals (which use optional witness data), NAT cannot be filtered without a Bitcoin hard fork. This is a genuine technical distinction: miners receive NAT by doing nothing differently. The protocol simply observes something that must already be in every block.

The honest case for NAT

NAT had a genuine fair launch. Its technical implementation is Bitcoin-native and requires no protocol change. Mining pools can adopt it at zero cost to themselves or their miners. The SEC's March 2026 guidance excluding proof-of-work mining rewards from securities classification reduces regulatory risk. The idea of a supplemental miner revenue stream that is unfilterable and permissionless is conceptually interesting.

The honest case against

NAT is down 96% from its all-time high. Its current contribution to block value is negligible. Trac Systems controls all TAP Protocol development and has hardcoded NAT as the only token that receives the miner subsidy, rejecting community proposals to open the mechanism. No public security audit has been conducted. The pseudonymous founder adds an accountability gap. The protocol produces continuous inflation with no burn mechanism.

Bitcoin maximalists, including developers like Luke Dashjr, consider meta-protocols such as TAP to be spam that should not be encouraged. This perspective has merit from a protocol-purity standpoint, even if the technical reality is that NAT cannot be filtered without changing Bitcoin itself. Reasonable people in the Bitcoin community disagree on whether meta-protocol activity is net positive or negative for the network.

What This Means for You