Both Ethereum and Solana use Proof of Stake (PoS): validators stake tokens to earn the right to produce and vote on blocks. The two chains diverge in how validators reach agreement and in how quickly a block becomes final. Ethereum finalizes blocks in epochs that take roughly 13 minutes, while Solana's Alpenglow consensus targets finality in about 150 milliseconds. This chapter covers how each chain gets there.
Ethereum's original consensus
Originally, Ethereum adopted the Proof of Work(PoW) method, which is still used by Bitcoin. After the Merge upgrade in September 2022, Ethereum transitioned from Proof of Work to Proof of Stake, and now employs PoS as mentioned above.
Ethereum's current consensus
At its core, Ethereum uses PoS through a consensus algorithm called Gasper, which combines Casper the Friendly Finality Gadget (Casper-FFG) with the LMD-GHOST fork choice rule. Since the Merge, a validator chosen from the staking set proposes each block, and proof of work plays no role in block production.
Casper (Casper-FFG), a part of Gasper, upgrades certain blocks to a "finalized" state, ensuring network participants are synchronized with the regular chain. It was initially proposed for the transitional phase from a PoW-based chain to PoS during the Merge upgrade and now contributes partially to the larger Gasper algorithm. LMD-GHOST (Latest Message Driven Greediest Heaviest Observed SubTree) is a fork choice algorithm used to select the most valid and trustworthy chain among various forks. In case of a fork generating multiple new blocks, validators vote through attestation messages to determine which block to append to the existing chain. These attestations follow a path from the genesis block to the latest block (leaf block), selecting the block backed by the most recent attestations.
Solana's consensus
Solana's consensus has changed more than Ethereum's. From mainnet launch, Solana ran Tower BFT, a variant of Practical Byzantine Fault Tolerance (PBFT) that used Proof of History (PoH) as a shared clock and had validators cast votes as onchain transactions. The Alpenglow upgrade replaces that voting layer, starting with Votor; a second protocol, Rotor, is planned for a later release.
Votor handles voting and finality. Validators send votes directly to one another instead of placing vote transactions inside blocks, and those votes aggregate into a stake-weighted certificate. A block finalizes in a single round when votes for it reach 80% of stake, or in a second round once 60% of stake has voted. This is the change that brings finality down to roughly 150 milliseconds.
Rotor is the planned second phase and is not live yet. Solana still propagates blocks with Turbine, its tree-based broadcast protocol; Rotor will replace it with a single relay layer that cuts the network hops between the leader and the rest of the validators.
Proof of History, the verifiable clock that Tower BFT depended on, is no longer part of how validators reach agreement. For most applications nothing changes: signing, sending, and reading transactions work as before, and finality simply arrives sooner. Validators that join Alpenglow consensus need a registered BLS public key and a client version that supports it.
Put side by side, Ethereum reaches finality by accumulating attestations across two epochs, while Solana reaches it by collecting a stake-weighted certificate within a slot:
| Ethereum | Solana |
| Proof of Work » Proof of Stake | Proof of Stake |
| Casper the Friendly Finality Gadget (Casper-FFG) | Votor certificates (finality in one or two rounds) |
| LMD-GHOST Fork Choice Rule | Votor votes (previously Tower BFT + PoH) |
| Gossip-based block propagation | Turbine (Rotor planned) |
Summary
- Ethereum's Consensus: PoS based Gasper = Casper the Friendly Finality Gadget (Casper-FFG) + LMD-GHOST Fork Choice Rule
- Solana's Consensus: PoS based Alpenglow: Votor (voting and finality) replaced Tower BFT + PoH; Turbine still handles block propagation until Rotor ships