Proof of stake

Proof of stake (PoS) is the consensus mechanism Ethereum and most new blockchains use to agree on the order of transactions, replacing the proof-of-work model Bitcoin still uses.

The basic idea: validators lock up cryptocurrency as a stake (currently 32 ETH per Ethereum validator). The protocol selects validators pseudo-randomly weighted by stake to propose and attest to new blocks. Validators earn fees and protocol rewards for honest participation. Validators who attempt to cheat (double-signing blocks, going offline for extended periods) lose part or all of their stake — “slashing.”

The security argument: an attacker who wants to corrupt the chain must accumulate enough stake to dominate validator selection (roughly 1/3 for liveness attacks, 2/3 for safety attacks). Acquiring that much stake is enormously expensive on a high-cap chain, and the moment the attack starts, the value of the stake itself collapses — making the attacker punish themselves.

Compared to proof-of-work, PoS:

• Uses dramatically less energy. Ethereum’s energy use dropped ~99.95% after switching from PoW to PoS in September 2022.
• Has lower hardware barriers. A validator is a normal computer; PoW needs ASIC farms.
• Concentrates differently. PoW concentrates in cheap-electricity regions. PoS concentrates in whales who hold large stake (or staking pools aggregating it).
• Allows in-protocol penalties. Slashing is a feature only PoS can really implement; PoW just lets cheaters fail to mine valid blocks.

Major PoS chains as of 2026: Ethereum (post-merge), Cardano, Solana, Polkadot, Cosmos, Tezos, Avalanche, plus essentially every new L1 launched after 2022. Bitcoin remains as the canonical PoW holdout.