Bitcoin has a maximum supply of 21 million BTC.
New bitcoins are issued through mining, with rewards decreasing through Bitcoin halving events.
As the supply limit is reached, block rewards will continue to decrease.
After all 21 million bitcoins are mined, miners can continue securing the network and processing transactions.
Transaction fees are expected to become an increasingly important part of the Bitcoin mining reward model.
Understanding Bitcoin supply, halving, mining rewards, and transaction fees helps explain Bitcoin's long-term network design.