In this lesson
- find out how Ethereum moved from mining to proof of stake
- understand what validators do and when they lose money
- learn what finality is and why it matters
Imagine swapping a plane's engines mid-flight – without the passengers even noticing. That is exactly what Ethereum did on 15 September 2022. A network full of money switched from mining to a completely different way of agreeing on blocks, and nobody had to get off.
The Merge#
From December 2020 a test "Beacon Chain" ran next to Ethereum, already using proof of stake. In The Merge the original network joined it and mining ended. Electricity use fell by roughly 99.95% – the miners' graphics cards disappeared overnight.
How validators work#
A validator locks up ETH as a deposit (the minimum is 32 ETH) and runs software that:
- proposes blocks – when it is its turn, it puts waiting transactions into a block,
- votes (attests) – every 6.4 minutes it confirms which block it considers valid.
Time moves in steps: a slot lasts 12 seconds and one block can be created in each. 32 slots make one epoch (6.4 minutes). Honest work earns the validator a reward in ETH.
Finality#
After about two epochs, so about 12.8 minutes, a block is final. Reverting it would destroy at least a third of all staked ETH. Exchanges, for example, wait for finality before they credit your deposit.
Slashing: the penalty for cheating#
A validator that signs two different blocks for the same slot or casts two contradictory votes gets slashed: it loses part of its deposit and is thrown out of the network. The more validators make the same mistake at the same time, the bigger the penalty. Simply being offline costs only a small penalty – about as much as the validator would have earned in that time.
Slashing is rare. A recent case: on 10 September 2025 39 validators were slashed because of a configuration error at their operator, not because of a bug in Ethereum.
Upgrades after The Merge#
| Upgrade | When | What it brought |
|---|---|---|
| Shapella | 12 Apr 2023 | withdrawals of staked ETH |
| Dencun | 13 Mar 2024 | cheap data storage for layer 2 networks ("blobs") |
| Pectra | 7 May 2025 | validators with up to 2,048 ETH, smart features for ordinary accounts |
| Fusaka | 3 Dec 2025 | more room for layer 2 data (PeerDAS), cheaper passkeys |
The next upgrade, Glamsterdam, has been running on a test network since 6 October 2026. A date for the main network has not been officially set yet (as of 11 October 2026).
Proof of stake has weak spots too
More ETH means more votes. Large staking providers and exchanges therefore control a significant part of the network. We get to it in the staking module.
Common myths#
- "The Merge made fees cheaper." It did not. It changed how blocks are made, not how much fits into them.
- "An offline validator can lose its whole deposit." Being offline costs a small penalty; slashing is for cheating or a broken setup.
- "Proof of stake is new and untested." It has run Ethereum since 2022 and secures over a hundred billion dollars.
Summary
- On 15 September 2022 Ethereum swapped mining for proof of stake; electricity use fell by 99.95%.
- Validators deposit ETH, propose blocks and vote; a slot lasts 12 s, an epoch 6.4 min.
- A block is final after about 12.8 minutes.
- Cheating leads to slashing, being offline only to a small penalty.