The Merge hard fork
Paris (execution) + Bellatrix (consensus) · Mainnet 2022-09-15
Proof-of-work mining ended and Ethereum moved to proof of stake. Ethereum's energy use fell by more than 99%.
What changed
- Users
- The way you sent transactions or used wallets stayed the same. Fees did not go down and processing did not get faster. Instead, the way the network is secured changed from mining hardware to staked ether (ETH), and electricity use fell by more than 99%. The interval between blocks, which had varied with mining luck, became fixed at one block every 12 seconds.
- Wallet & app developers
- Smart contracts and APIs mostly kept working as before. What changed is the DIFFICULTY opcode. With mining difficulty gone, the beacon chain's random value (PREVRANDAO) took its place. Contracts that used Solidity's block.difficulty as a difficulty number, or assumed it was a small value, started receiving a completely different value. This value can be used as a reference for things like lotteries, but the block proposer can know it one slot ahead, so it is best not to use it as is for lotteries with large sums at stake. With block intervals fixed at 12 seconds, it became easier to predict when a transaction would be finalized.
- Validators
- Validators took over the role of miners. By depositing 32 ETH and running validator software, they propose blocks, vote on other blocks, and earn rewards. Validators that, before The Merge, only took part in consensus on the Beacon Chain began producing blocks that include execution layer transactions from this day. Transaction fee tips and MEV revenue also went to validators instead of miners. Withdrawals of staked ether and rewards were not open at the time of The Merge and became possible in the next upgrade, Shapella.
- Node operators
- A setup that used to be a single node became two. You have to run a consensus client (Prysm, Lighthouse, etc.) alongside the existing execution client (Geth, etc.), and the two are connected through the Engine API, which is authenticated with a JWT secret. Without a consensus client, the execution client cannot receive new blocks and the chain appears to have stopped. Mining-related settings from the proof-of-work era and sync decisions based on difficulty no longer have any meaning.