The 21 Million Cap

What enforces the limit on new bitcoin?

• A company that licenses the Bitcoin software
• Every full node, which rejects any block that pays its miner more than the rules allow
• The miners, who agree each year on how many coins to create

Each era is 210,000 blocks and the subsidy halves each time. What happens to the amount of new bitcoin each era creates?

• It stays the same, because each era has the same number of blocks
• It halves, because the same number of blocks each pay half as much
• It doubles, to make up for the smaller subsidy