It's not code. It's not nodes. It's money.
Bitcoin is secured by miners who get paid through block rewards and transaction fees. Together these form the security budget. Lyn Alden establishes that this budget must stay above 0.5% of market cap to keep the network safe — today it's ~0.8%, but after the 2028 halving it drops to 0.4% from block rewards alone, regardless of price. From that point, fees must make up the difference or security erodes. People say "the last bitcoin won't be mined until 2140" — technically true, but the block reward becomes irrelevant a century before that.
See the math →Drag the sliders and watch the security budget collapse.
The only other source of miner income is transaction fees.
Bitcoin processes roughly ~500,000 transactions per day at full capacity. The question is: will people pay enough in fees to fund the security budget?
Set the year to 2040. Now crank Bitcoin's price to $1M. See how small the block reward bar gets? Now slide the fee rate up. That's the only lever left. Without meaningful fees, the security budget collapses no matter what the price does.
Every halving, the gap between what miners need and what they get grows wider.
Bitcoin's security doesn't come from its price. It comes from what miners get paid. And what miners get paid is about to change fundamentally.
By 2040, the block reward drops to ~28 BTC/day. Even at $1,000,000/BTC, that's only $28M/day in miner revenue from block rewards alone.
Today, miners earn ~$30M/day from block rewards at ~$67K/BTC.
Price going up 10x doesn't even maintain the current security level past a few more halvings. That's the counterintuitive part.
The only path forward is a robust fee market. Transactions must generate enough revenue to replace what the block reward can no longer provide.
This isn't FUD. This is math. And it's the single most important long-term question facing Bitcoin.
Lyn Alden — "Bitcoin: Fee-Based Security Modeling"
The most comprehensive analysis of Bitcoin's long-term security economics.