Beacon Block

A Beacon Block is the core data unit produced by validators on the Ethereum Beacon Chain, containing the consensus-critical information necessary to advance the state of the Proof-of-Stake (PoS) network. Each block includes an execution payload header (a summary of transactions from the Execution Layer), a list of attestations (votes on chain head and justification), and details of validator operations like slashings and deposits. It is proposed by a randomly selected validator committee approximately every 12 seconds, forming the immutable ledger of the consensus layer.

The structure of a Beacon Block is defined by the Ethereum consensus specifications. Key components are the slot number (its position in the blockchain), the proposer_index (the validator who created it), the parent_root (a cryptographic link to the previous block), and the state_root (a hash representing the entire Beacon State). This rigorous structure allows all network participants to independently verify the block's validity and the state transitions it causes, ensuring the security and finality of the chain without relying on external data.

Beacon Blocks are distinct from Execution Blocks, which contain the actual transaction data. This separation is the core of Ethereum's post-Merge architecture. The Beacon Block's execution payload header points to an Execution Block, creating a secure link between the consensus and execution layers. Validators attest to Beacon Blocks, and only after a block is finalized by the consensus layer are the transactions within its referenced Execution Block considered irreversible.

The process of creating a Beacon Block involves LMD-GHOST and Casper FFG fork-choice rules. When a validator is selected to propose a block, it gathers the latest attestations from peers, includes a new execution payload header from the connected execution client, and signs the assembled block. Other validators then attest to this block if it represents the canonical chain according to the fork-choice rule, gradually building consensus through cryptographic aggregation of votes.

Understanding Beacon Blocks is essential for analyzing Ethereum's security, validator rewards, and chain finality. Metrics like block propagation time, attestation inclusion delay, and reorg depth are derived from Beacon Block data. For developers, interacting with Beacon Chain data via APIs (like the Beacon Chain API) requires familiarity with this block structure to query validator performance, sync the consensus client, or monitor network health.

A beacon block is a data structure produced by a randomly selected validator every 12 seconds, forming the core of the Ethereum Beacon Chain's consensus layer. Unlike execution blocks that contain user transactions, a beacon block's primary function is to manage the proof-of-stake protocol. It achieves this by containing critical consensus data, including attestations (votes on chain head and justification), information about newly active and exiting validators, and a reference to the corresponding execution block via the execution_payload field. This separation of consensus and execution is the foundation of Ethereum's post-Merge architecture.

The creation of a beacon block follows a strict, slot-based schedule. Each slot (12 seconds) presents an opportunity for a single validator to propose a block. The proposer is chosen via the RANDAO-based randomness of the protocol. The block's contents are largely assembled from messages gossiped across the peer-to-peer network, primarily attestations from committees of validators attesting to the validity of the chain head and the current epoch's checkpoint. By aggregating these votes, the beacon block drives the fork choice rule (LMD-GHOST) and finalizes epochs, ensuring all nodes agree on the canonical chain.

Key components within a beacon block include the state_root, a cryptographic commitment to the entire Beacon State after applying the block's changes; the body, which houses the lists of attestations, deposits, and other operations; and the aforementioned link to the execution layer. This design ensures the consensus layer remains lightweight and focused on security, while delegating complex transaction processing to the parallel execution layer. The integrity of each block is secured by the proposer's BLS signature.

From a node's perspective, processing a beacon block involves verifying all signatures, checking the validity of the proposed state transition, and ensuring the block builds on the justified checkpoint as defined by the fork choice rule. Successful validation leads the node to update its local copy of the Beacon State and gossip the block to its peers. This continuous, slot-by-slot production and validation of beacon blocks is what maintains the liveness and finality guarantees of the Ethereum network under proof-of-stake, making it resistant to chain reorganizations and ensuring a single, agreed-upon history.

A Beacon Block is the fundamental unit of data produced by the Beacon Chain, containing the critical information necessary to achieve consensus and finalize the state of the Ethereum network. Unlike execution blocks that process user transactions, a Beacon Block's primary role is to orchestrate the consensus mechanism itself. It is proposed by a randomly selected validator every 12 seconds and includes attestations (votes on chain head and justification), information about new validators, and a reference to an execution payload from the execution layer.

The structure of a Beacon Block is defined by the consensus layer specifications. Its key components are the body, which houses the BeaconBlockBody, and the slot number indicating its position in the blockchain. The block body contains aggregated attestations from committees of validators, proposer slashings and attester slashings for penalizing malicious actors, and the crucial link to the corresponding execution block via the execution_payload_root. This separation of concerns between consensus and execution is the architectural foundation of Ethereum's post-merge design.

The creation and propagation of a Beacon Block is central to the LMD-GHOST and Casper FFG hybrid consensus protocol. When a validator is selected as a block proposer, it gathers the latest attestations, aggregates them, and packages them into a new Beacon Block. Other validators then attest to this block, forming a cryptographic proof of its validity and the chain's current state. This continuous cycle of block proposal and attestation drives the finality of the chain, ensuring that once a block is finalized, it is extremely costly and practically impossible to revert.

The Merge refers to the specific moment when Ethereum's original Execution Layer (the Mainnet) merged with the new Consensus Layer (the Beacon Chain), permanently retiring Proof-of-Work (PoW) mining. This event, executed in September 2022, marked the completion of Ethereum's transition to a Proof-of-Stake (PoS) consensus mechanism. The primary objectives were to drastically reduce energy consumption (by over 99%), enhance network security through economic finality, and lay the foundational infrastructure for future scalability upgrades like sharding.

In the post-Merge architecture, validators replaced miners as the network's block producers. Validators are required to stake a minimum of 32 ETH to participate in proposing and attesting to blocks. The network's security is now derived from this staked capital, with penalties (slashing) for malicious behavior. The fork choice rule, which determines the canonical chain, is governed by the LMD-GHOST algorithm, which considers the accumulated votes (attestations) of validators rather than computational work.

A key technical outcome was the separation of concerns into two primary layers. The Consensus Layer (Beacon Chain) is responsible for organizing validators, managing the consensus protocol, and achieving finality. The Execution Layer handles transaction execution, state management, and runs the Ethereum Virtual Machine (EVM). These layers communicate via the Engine API, where the consensus client (e.g., Prysm, Lighthouse) proposes a slot for a block, and the execution client (e.g., Geth, Nethermind) supplies the transaction payload.

The post-Merge era introduced new concepts like slot and epoch. A slot is a 12-second period in which a single validator is expected to propose a block. An epoch consists of 32 slots (approximately 6.4 minutes) and is the unit at which validator committees are reassigned and attestations are finalized. Finality is now cryptoeconomic: after two epochs, a block is considered finalized if supported by a supermajority of validators, making reversion prohibitively expensive and providing stronger security guarantees than probabilistic finality under PoW.

This new architecture is the essential prerequisite for Ethereum's ongoing scalability roadmap. The Merge's PoS foundation enables Danksharding, a design where the Beacon Chain and validators will also coordinate and validate data availability for Layer 2 rollup chains. This separates data publication from execution, allowing rollups to post cheap data to Ethereum while performing computation off-chain, scaling the network's throughput by orders of magnitude without compromising decentralization.