On what date did Ethereum’s network switch from proof of work to proof of stake?

Ethereum switched from proof of work to proof of stake on 15 September 2022.

The upgrade was called The Merge because Ethereum’s original execution layer was combined with the Beacon Chain, a proof-of-stake coordination layer that had operated separately since December 2020. After The Merge, Ethereum’s consensus was secured by validators who deposited ether rather than by miners competing with computing power.

The change substantially altered Ethereum’s energy model and ended proof-of-work mining on the main network. It did not create a new cryptocurrency or erase existing balances; the chain’s historical state continued through the upgrade.

The Merge is sometimes confused with later scaling upgrades. It changed consensus, while upgrades such as the Shanghai/Capella upgrade later enabled validator withdrawals and other changes.