What was the Ethereum Merge?

The Ethereum Merge was the upgrade that switched Ethereum from proof of work to proof of stake by joining two chains into one. Ethereum's original network, which held every account, contract and transaction, stopped relying on miners and began taking its blocks from the Beacon Chain, a proof of stake chain built for the purpose. It went live on September 15, 2022, and ether holders did not need to do anything.

What was the Merge on Ethereum?

ethereum.org describes the change as merging two layers. The execution layer is the part users touch, where transactions run and balances live. The consensus layer is the Beacon Chain, where validators who have staked ether agree on which blocks are valid.

Before the Merge, those two ran side by side but separately. Afterwards, the original chain's history and state carried on unchanged, but its blocks were produced and confirmed by the Beacon Chain. No new coin was created, and ethereum.org warns that anyone claiming ETH had to be swapped or upgraded was likely running a scam. The guide to proof of work vs proof of stake explains the two systems.

When was the Ethereum Merge?

The Beacon Chain launched on December 1, 2020, and ran in parallel with mainnet for almost two years. The Ethereum Foundation then scheduled the switch in two parts.

• Bellatrix, an upgrade to the Beacon Chain, activated on September 6, 2022.
• Paris, the actual handover on the execution side, was set to trigger once mining reached a terminal total difficulty, a fixed amount of cumulative mining work. Because hash rate varies, the foundation could only give a window of September 10 to 20.

The trigger was hit and the Merge completed on September 15, 2022.

What changed after the Ethereum Merge?

Block production moved from miners to staked validators, which is why Ethereum can no longer be mined. Blocks now come in 12-second slots, against roughly 13.3 seconds on average under mining, and ethereum.org notes the network gained finality, with blocks grouped into 6.4-minute epochs that validators vote to finalize. Every node operator must now run two pieces of software together, an execution client and a consensus client, and stakers must set an address to receive transaction fees.

ethereum.org lists several things the Merge did not do. It did not lower gas fees, because it changed how blocks are agreed on rather than how much they hold. It did not make transactions much faster. It also did not let stakers withdraw their ether. Withdrawals came with a later upgrade, Shapella, which The Block reported core developers had set for April 12, 2023.

Energy use fell by more than 99.9%, and ether issuance fell sharply once miners no longer had to be paid. Our guide on whether Ethereum is deflationary covers the supply effects.