The London Harfork (August 2021) changed Ethereum's fee market and introduced the burn rate.

Ethereum fees are split into base fees and priority fees. The base fee is determined by the protocol and changes accordingly to the network demand, expressed in dynamic block sizes. Priority fees are optional and can be paid to have transactions processed faster. The upgrade introduced a fee-burning mechanism, where the base fee is burnt, laying the groundwork for the ETH supply to become deflationary.

With the Merge in September 2022, Ethereum will make the final switch from Proof-of-Work to Proof-of-Stake. From that point on, the issuance of ETH will be determined solely by validator rewards, while the burn rate remains the same. It is at this moment that ETH potentially becomes deflationary.