The Merge — Ethereum moves to proof-of-stake

On September 15, 2022, Ethereum replaced its consensus engine while running — swapping proof-of-work mining for proof-of-stake, with billions of dollars riding on it, and not dropping a block. It's arguably the most ambitious live upgrade in the history of software.

What actually changed

BEFORE                     AFTER (The Merge)
 execution layer            execution layer  (unchanged for users)
      ↑                          ↑
 proof-of-WORK   ──────────→ proof-of-STAKE (Beacon Chain)
 miners + GPUs              validators + 32 ETH stake
 ~110 TWh/yr                ~0.01 TWh/yr  (−99.9%)

Your transactions, contracts and addresses didn't change. Under the hood, security stopped coming from burning electricity and started coming from staked capital that can be slashed for misbehavior.

Why it was a milestone

What it didn't do

A common misconception at the time: that the Merge would make gas cheap. It didn't — it changed *how* blocks are produced, not *how much* blockspace exists. Fees are a scaling problem, and the answer to that is the rollup roadmap (blobs), not the consensus swap. The Merge was about security and sustainability, not throughput.

Stake instead of electricity

Under proof-of-stake a validator locks 32 ETH and attests to blocks. Misbehave — double-sign, or go offline at the wrong moment — and the protocol slashes part of that stake. Security stops being "whoever burns the most electricity" and becomes "whoever has the most capital at risk of being destroyed for cheating." Attacking the chain means putting your own stake on the bonfire.

Beyond the ~99.9% energy cut, the Merge set up everything after it: issuance dropped (combined with 1559's burn, ETH trends deflationary), and proof-of-stake is the substrate that makes blobs, danksharding and the rollup roadmap possible.