The issuance of Ethereum in Proof-of-Stake (POS) is determined by the percentage of ETH staked. Currently, the issuance rate is set at 1.5%, meaning that for every 100 ETH staked, 1.5 ETH is issued. This is a more simple approach than the previous model of 5% emission with an additional 0.5% deflation for delegators, which can be confusing to understand. This dynamic approach allows for the issuance rate to adjust based on the amount of ETH staked, meaning that the more ETH that is staked, the lower the issuance rate. This helps to ensure that the network is secure, while also providing rewards to stakers.