The Merge

The Merge was the moment in September 2022 when Ethereum stopped using proof of work and switched to proof of stake. A separate proof-of-stake chain had been running alongside since 2020; at the Merge, the main Ethereum network joined onto it.

Overnight, miners were out and validators were in. Ethereum's energy use fell by more than 99%, and the flood of new ETH paid to miners dried up. The switch went smoothly despite years of warnings that it might not, and the many GPU miners had to move to other coins or switch off.