Bitcoin‑Style Competition Among Ethereum Builders: A Complete Guide to the ePBS Architecture
※ This article is being published in its current draft form and will be updated to the final Daily Crypto Times (DCT) format in 2 days.
Ethereum’s Glamsterdam Upgrade: How ePBS Opens a New Block Production Structure
CoinMarketCap recently shared the following update:
“Ethereum's Glamsterdam upgrade is now in its final development phase ahead of testnet deployment, with a mainnet launch expected in H2 2026.”
Glamsterdam is not just another feature upgrade — it is a major redesign of Ethereum’s block production structure at the protocol level. At the heart of this change is ePBS (Enshrined Proposer‑Builder Separation). ePBS brings the previously external MEV-Boost–based block building process into the protocol itself and clearly separates the roles of Proposer and Builder, fundamentally improving censorship resistance, decentralization, and the MEV landscape.
This article is best read together with the earlier piece, “How Focil and ePBS Are Rewriting Ethereum’s Block Production Pipeline” , which explains the broader restructuring of the block production pipeline. In particular, if you also refer to “Ethereum’s Block Reborn: Why FOCIL and ePBS Completely Redesign the Slot Structure” , you’ll get a clearer picture of the philosophy and problem framing behind the Glamsterdam upgrade.
1) How does the Proposer receive and verify the Builder’s Payload in ePBS?
Under ePBS, block production is split between two distinct roles:
- Builder: The actor that constructs the Execution Payload (a bundle of transactions).
- Proposer: The actor that selects one Payload from multiple Builders and finalizes the block.
A key question here is: When and how is the Proposer selected?
The Proposer is automatically chosen by the Beacon Chain (Consensus Layer) for each slot.
Slots are roughly 12 seconds long, and for each slot, a Proposer is randomly selected from the validator set and granted the right to propose exactly one block in that slot.
In other words, the Proposer is a protocol-elected, official role.
① Builder → Proposer: Submitting the Payload
The Builder sends its constructed Execution Payload to the Proposer.
The Payload includes the transaction list, the state root, and the bid (the reward the Builder offers to the Proposer).
Multiple Builders can submit Payloads to the Proposer at the same time.
② Proposer receives Payloads over the network
The Proposer receives Payloads from Builders via the ePBS interface.
Once a slot starts, the Proposer listens for all Payloads arriving during that slot.
Builders need to submit their Payloads as quickly as possible to stay competitive.
③ Execution Client verifies Payload validity
The Proposer must ensure that a Payload is actually executable as a block.
To do this, it asks its Execution Client to verify the Payload. The Execution Client checks:
- Transaction validity
- Correctness of the state transition
- Whether the state root matches
- Whether gas limits and protocol rules are respected
④ Proposer selects the Payload with the highest reward
Among all valid Payloads, the Proposer selects the one with the highest bid (reward) offered by a Builder.
The Proposer receives this bid as its block proposal reward.
⑤ The selected Payload is included in the Beacon Block
The Proposer then includes the chosen Payload in the Beacon Block and finalizes the block.
Validators subsequently attest to this block as part of the consensus process.
Summary: For each slot, the Proposer is automatically selected by the Beacon Chain, receives Payloads from Builders, verifies them via its Execution Client, and includes the Payload that offers the highest reward.
2) Comparing Builder Payload competition to Bitcoin mining
The way Builders compete in ePBS is strikingly similar to how Bitcoin miners compete. Both follow the same timing model: “round-based competition → one winner → everyone else stops immediately.”
Also, unlike the Proposer, the Builder is not a protocol-assigned role — it is a market participant that joins voluntarily for economic incentives. The main incentives for Builders are:
- Maximizing MEV (Maximal Extractable Value) revenue
- Winning the block by bidding to the Proposer
- Leveraging economies of scale to capture more MEV
① When does the competition start?
Bitcoin miners: Start mining when a new block height becomes available.
Ethereum Builders: Start constructing Payloads when a new slot begins.
② What happens during the competition?
Bitcoin miners: Continuously tweak the nonce to solve the PoW puzzle and rebuild block candidates as needed.
Builders: Continuously monitor the mempool, search for MEV opportunities, rebuild Payloads, and submit them to the Proposer.
③ When does the competition end?
Bitcoin miners: Stop mining immediately when another miner finds a valid block.
Builders: Immediately discard their Payloads in the following situations:
- The Proposer has already selected another Builder’s Payload.
- The slot has ended.
- Another Builder has won with a higher bid.
④ Side-by-side comparison
| Aspect | Bitcoin Miner | Ethereum Builder (ePBS) |
|---|---|---|
| Competition start | New block height | New slot |
| Competition mechanism | PoW hash puzzle | MEV-based Payload construction |
| Goal | Find a valid block hash | Be selected by the Proposer |
| Competition end | Another miner finds a block | Proposer selects another Payload |
| On losing | Immediately stop mining | Immediately discard the Payload |
| Next round | Start at the next height | Start at the next slot |
Conclusion: The core of Glamsterdam is “enshrined ePBS”
The Glamsterdam upgrade is a fundamental redesign of Ethereum’s block production at the protocol level.
- The Proposer is an official role automatically selected by the Beacon Chain for each slot.
- The Builder is a market participant that competes for MEV revenue.
- The Proposer receives and verifies Payloads from Builders and selects the one with the highest reward.
- The Builder competition model closely resembles Bitcoin’s mining competition — a round-based race with a single winner.
This architecture is a key step toward Ethereum’s long-term goals of stronger censorship resistance, reduced Builder centralization, and greater MEV transparency. With Glamsterdam expected to hit mainnet in the second half of 2026, Ethereum is on the verge of entering a new era in block production.
Younchan Jung
Researcher exploring structural shifts in AI, blockchain, and the on‑chain economy.
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