Block Proposer in Ethereum

The validator pseudo-randomly selected to propose and broadcast a new block during a specific 12-second slot in Ethereum’s proof-of-stake consensus mechanism.

What is a Block Proposer in Ethereum?

In Ethereum’s proof-of-stake (PoS) system, a block proposer is a specific validator node, operated by a user who has staked at least 32 ETH (Ethereum’s native digital asset), chosen to construct and submit a new beacon block for inclusion in the blockchain during an assigned slot. Slots last 12 seconds, with 32 slots forming an epoch of approximately 6.4 minutes. Selection occurs pseudo-randomly via RANDAO, an algorithm that mixes hashed commitments from validators with a seed value to ensure unpredictability, weighted by the validator’s effective balance (capped at 32 ETH for fairness). This selection is determined two epochs in advance to prevent manipulation of the randomness seed. Only one proposer per slot is chosen, and attempting to propose multiple blocks in the same slot results in slashing, where the validator loses part or all of their staked ETH as a penalty.

The block proposer’s primary responsibilities include gathering and including various data in the beacon block, such as a RANDAO reveal for randomness, eth1_data voting on deposit contract state, proofs of slashing offenses by other validators, new deposits, voluntary exits, sync committee attestations, and an execution payload containing transactions and state changes from the execution layer. The proposer must build the block atop the chain’s current head according to their local fork choice rule and broadcast it via the consensus layer’s gossip network for attestation by other validators. If the proposer is offline or fails to act, the slot remains empty, though the chain progresses.

Block proposers earn rewards including a base reward proportional to the number of active validators and their balances, plus a share of attestation rewards for timely inclusions, and bonuses for reporting slashed validators (1/512 of their effective balance per report). As of September 2025, Ethereum is preparing for Proposer-Builder Separation (PBS) in the upcoming Scourge upgrade, which will evolve the proposer’s role to auction and select pre-built execution payloads from specialized builders to enhance MEV resistance and decentralization, rather than constructing them directly.