How Does the Security Budget of Bitcoin Change over Time?

The Bitcoin security budget is the total revenue earned by miners (block rewards plus transaction fees), which incentivizes them to secure the network. Over time, the block reward decreases due to halving, causing the security budget to rely increasingly on transaction fees.

The long-term security of the network depends on transaction fees growing sufficiently to compensate for the diminishing block rewards, ensuring the economic cost of a 51% attack remains prohibitively high.