The Merge was the upgrade that moved the Ethereum blockchain from proof of work, in which miners compete with computing power to add blocks, to proof of stake, in which validators who lock up ether take turns proposing and confirming blocks. It took place on 15 September 2022, when Ethereum's original chain was combined with the Beacon Chain, a separate proof-of-stake chain that had been running alongside it since December 2020. From that moment, mining ether was no longer possible.
The Merge was the result of years of research and is widely regarded as one of the most complex upgrades ever made to a live blockchain. It was long promoted under the banner "Ethereum 2.0", a label the Ethereum Foundation dropped in early 2022 in favour of describing the network as having an execution layer and a consensus layer. The Merge is the first of the named stages in Ethereum's roadmap, followed by others including the Surge.
The Merge in plain terms
Think of an aircraft whose engines are replaced in mid-flight. Passengers stay in their seats, their luggage remains on board, and the plane keeps flying on the same route, but the noisy, fuel-hungry engines are swapped for quieter, more efficient ones without landing.
That was the Merge. All the accounts, balances, smart contracts and transaction history on Ethereum stayed exactly as they were. What changed was the machinery that decides who gets to add the next page to the shared record. Instead of thousands of miners racing powerful computers against each other, the job passed to validators who have put up ether as a deposit and who can lose part of it if they cheat.
How the Merge worked
Before the Merge, Ethereum effectively ran two chains. The original chain processed transactions and smart contracts and was secured by miners using the Ethash algorithm. The Beacon Chain, launched on 1 December 2020, ran proof-of-stake consensus among validators who had each deposited 32 ether, but it carried no user transactions.
- Testing. The switch was rehearsed through shadow forks and on several public testnets during 2022.
- Consensus upgrade. An upgrade to the Beacon Chain, named Bellatrix, prepared validators for the switch in early September 2022.
- The trigger. Rather than a fixed block number, the Merge was set to happen when the proof-of-work chain reached a chosen level of total accumulated mining difficulty, which occurred on 15 September 2022.
- The handover. From that block on, the execution layer stopped accepting mined blocks and followed the Beacon Chain, whose validators now proposed and attested to every block.
Node operators had to run two pieces of software side by side, an execution client and a consensus client, a structure that remains in place.
Effects of the Merge
- Energy use. The Ethereum Foundation estimated that the change cut the network's energy consumption by more than 99.9 per cent, removing the main environmental criticism of Ethereum.
- Issuance. Ending mining rewards reduced the amount of new ether created by roughly 90 per cent. Combined with the burning of part of each transaction fee, introduced in 2021, this means ether's supply can shrink in periods of high activity, though it has also grown at other times.
- Security model. Network security now depends on the value of staked ether and on penalties such as slashing for dishonest validators.
- Block timing. Blocks moved to a regular schedule of one slot every 12 seconds.
Former Ethereum miners had to stop or move their hardware to other networks. Some supported a proof-of-work fork of Ethereum, while others moved to Ethereum Classic, which kept proof of work.
What the Merge did not do
The Merge did not lower transaction fees or noticeably increase the network's capacity; those goals belong to later roadmap stages focused on rollups and data availability. It also did not allow stakers to withdraw their deposited ether. Withdrawals became possible only with the Shanghai upgrade in April 2023, which removed one of the main risks of staking.
Criticism and debate
Supporters praised the Merge as a technical success that happened without downtime. Critics raised concerns about concentration: large exchanges and liquid staking providers came to control a large share of staked ether, raising questions about censorship and decentralization. Some argued that proof of stake favours those who already hold the most tokens. The switch also revived debates about whether ether might be treated as a security in the United States, since holders could now earn rewards by staking, though US regulators did not reach a settled position at the time. As of November 2026, Ethereum continues to run on proof of stake, and many of these debates remain open.