Block Production

What Is Block Production?

Block production is the process of creating a new block of transactions and appending it to a blockchain. Every blockchain network needs a mechanism for deciding which pending transactions get included in the next block, how those transactions are ordered, and who earns the right to publish the result. The entity responsible for this work is called a block producer: a miner in proof-of-work systems or a validator (proposer) in proof-of-stake systems.

Block production sits at the core of how blockchains function. Without it, transactions would remain unconfirmed in the mempool indefinitely. The rules governing block production determine a network's throughput, finality guarantees, censorship resistance, and economic incentives for participants.

How It Works

Although implementation details vary across chains, block production follows a common lifecycle:

1. Transaction selection: the block producer pulls pending transactions from the mempool, typically prioritizing those with higher fee rates to maximize revenue
2. Block assembly: selected transactions are ordered and bundled together with metadata including the previous block header hash, a timestamp, and a Merkle root that cryptographically commits to every transaction in the block
3. Consensus work: the producer performs whatever work the consensus mechanism requires: solving a hash puzzle (PoW) or signing and broadcasting a proposal (PoS)
4. Propagation: the completed block is broadcast to the peer-to-peer network, where other nodes perform block validation before accepting it into their local copy of the chain

The block producer earns a block reward (the subsidy plus transaction fees) for successfully adding a valid block. This incentive structure is what motivates miners and validators to perform the work.

Block Header Structure

In Bitcoin, the block header is an 80-byte structure containing six fields that the miner hashes repeatedly while searching for a valid nonce:

Block Header (80 bytes)
├── Version          (4 bytes)  — consensus rules the block follows
├── Previous Hash    (32 bytes) — SHA-256d of the prior block header
├── Merkle Root      (32 bytes) — single hash committing to all transactions
├── Timestamp        (4 bytes)  — Unix epoch time when mining began
├── nBits            (4 bytes)  — compact encoding of the difficulty target
└── Nonce            (4 bytes)  — counter incremented during mining

The miner computes SHA-256(SHA-256(header)) and checks whether the resulting hash falls below the difficulty target encoded in the nBits field. If not, the nonce is incremented and the process repeats billions of times per second across the network.

Block Production in Bitcoin

In Bitcoin's proof-of-work system, block production is synonymous with mining. Miners compete to find a valid hash, and the winner publishes the next block. However, who actually decides which transactions go into that block is a separate and increasingly important question.

Block Templates and Mining Pools

Most miners participate in mining pools rather than mining solo. Historically, the pool operator constructs the block template: the ordered list of transactions and the block header that miners hash against. Individual miners in the pool receive this template and perform the hash computation without choosing which transactions to include.

The getblocktemplate RPC is Bitcoin Core's native interface for requesting a block template. A full node running getblocktemplate selects transactions from its mempool by ancestor feerate, constructs the Merkle tree, and returns a template that a miner can immediately begin hashing. Under the original Stratum protocol (v1), pools perform this step centrally and distribute the result to all connected miners.

This creates a centralization concern: the top four mining pools (including Foundry USA and AntPool) collectively produce roughly 70% of all Bitcoin blocks. Since pool operators build the templates, a small number of entities effectively control transaction selection for most of the network's block space.

Stratum V2 and Miner-Built Templates

Stratum V2 introduces a Job Negotiation Protocol that lets individual miners construct their own block templates. Instead of accepting the pool's transaction selection, a miner running a full node builds a template from its own mempool and proposes it to the pool. The pool validates the proposed template and credits the miner's work.

As of mid-2026, pools representing roughly 75% of global hashrate have joined the Stratum V2 Working Group, and the first miner-constructed block template has been successfully mined in a production pool. This shift pushes transaction selection back to individual miners, reducing the pool operator's control over block content.

Block Production in Ethereum

Since the Merge in September 2022, Ethereum uses proof-of-stake for block production. Every 12 seconds (one slot), the Beacon Chain pseudorandomly selects one validator as the block proposer. That validator assembles a block from pending transactions, signs it, and broadcasts it for attestation by a committee of other validators.

Proposer-Builder Separation

In practice, most Ethereum validators no longer build their own blocks. Proposer-builder separation (PBS) splits block production into two specialized roles:

• Builders are entities that construct blocks optimized for maximal extractable value (MEV). They order transactions to capture arbitrage, liquidations, and other value opportunities, then bid to have their block selected.
• Proposers (validators) receive sealed bids from builders via relays and select the highest bid. The proposer earns the bid payment without needing to understand MEV strategies or run sophisticated ordering algorithms.

The current implementation relies on MEV-Boost, an out-of-protocol middleware run by over 90% of Ethereum validators. Trusted relays sit between builders and proposers, verifying that submitted blocks are valid before forwarding them.

Builder concentration is significant: as of early 2026, two builders (Titan Builder and Beaverbuild) construct approximately 86% of MEV-Boost blocks. This level of concentration gives a small number of entities substantial influence over transaction ordering and inclusion.

Enshrined PBS (EIP-7732)

EIP-7732 proposes to move PBS into the consensus layer itself, eliminating the need for trusted relays. Under enshrined PBS (ePBS), the builder commitment and payload delivery become part of the protocol's fork choice rules. This aims to reduce trust assumptions and make builder selection more decentralized, though research suggests it may also amplify profit concentration among dominant builders.

Centralized vs. Decentralized Block Production

The degree of centralization in block production determines how resistant a network is to transaction censorship. Two models represent the spectrum:

Why Block Production Matters

Block production is not just a technical implementation detail: it defines the economic incentives, security guarantees, and neutrality of a blockchain. Several real-world consequences flow from how blocks are produced:

• Fee markets and user costs: block producers prioritize high-fee transactions, creating a fee market that determines how much users pay for timely inclusion
• MEV and fairness: the order in which transactions appear within a block can be worth significant value, and whoever controls ordering captures that value
• Network security: block rewards (subsidy plus fees) fund the security budget that protects the chain against attacks
• Layer 2 dependence: protocols like Spark, the Lightning Network, and rollups all depend on reliable layer 1 block production for settlement, force-close transactions, and data availability

For a deeper analysis of how mining pool concentration affects Bitcoin's block template process, see the research article on block template mining centralization. For Ethereum's MEV dynamics, see MEV and proposer-builder separation.

Risks and Considerations

Censorship

When block production is concentrated among a few entities, those entities can censor transactions by refusing to include them. On Ethereum, a dominant builder could exclude transactions from sanctioned addresses or competing protocols. On Bitcoin, a pool controlling significant hashrate could delay confirmation of specific transactions. The defense in both cases is a sufficiently decentralized set of block producers: even if one censors, others will include the transaction.

MEV Extraction

Block producers who control transaction ordering can extract value through front-running, sandwich attacks, and arbitrage. PBS was designed to separate the right to order transactions (builders) from the right to propose blocks (validators), but in practice the builder market has itself become highly concentrated. Mitigations under active research include inclusion lists (EIP-7805/FOCIL), partial block auctions, and encrypted mempools.

Single Points of Failure

In Ethereum's current PBS architecture, relays are trusted intermediaries between builders and proposers. A relay outage or a malicious relay can disrupt block production for validators that depend on it. Enshrined PBS aims to remove this dependency, but introduces its own complexity at the protocol level.

Mining Pool Centralization

In Bitcoin, the top mining pools produce a disproportionate share of blocks. While individual miners can theoretically switch pools, coordination costs and economic incentives keep hashrate concentrated. Stratum V2's miner-built templates are the primary mitigation, returning transaction selection to individual miners even within centralized pools.

This glossary entry is for informational purposes only and does not constitute financial or investment advice. Always do your own research before using any protocol or technology.