Currently only 850,000 Pluton are in circulation, and over the course of 150+ years the rest will be emitted for rebates via a smart contract until all 20,000,000 Pluton are in circulation. The exact duration will vary based on demand. This means that every time you make a deposit with Bitcoin or Ethereum, you will earn a small amount of PLU as a rebate. Only 20,000,000 PLU will ever be issued, and any further issuance will be impossible. An updated calculator for PLU emission is available on the Plutus website.