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Ethereum's Glamsterdam Upgrade: How ePBS and EIP-7732 End the Flashbots Era and Rewrite MEV

· 9 min read
Dora Noda
Dora Noda
Software Engineer

Two companies currently decide which transactions land on Ethereum. Titan Builder and Beaverbuild together construct roughly 86% of mainnet blocks, and adding Rsync and Flashbots pushes the top four past 90%. For a network whose brand rests on decentralization, that is an uncomfortable number — and it is about to change.

The Glamsterdam hard fork, scheduled for the first half of 2026, brings Enshrined Proposer-Builder Separation (ePBS) — formalized as EIP-7732 — into Ethereum's consensus layer. After three years of MEV-Boost running as off-chain middleware, block production is finally being absorbed into the protocol itself. The winners and losers of that shift will define the next cycle of Ethereum infrastructure.

The Duopoly Problem Glamsterdam Is Trying To Solve​

To understand why ePBS matters, start with the market it is replacing.

MEV-Boost, the relay system Flashbots shipped after The Merge, was meant to be a temporary fix. It let validators outsource block construction to specialized builders who could squeeze more value out of each slot, then redistribute that value back to the proposer. It worked almost too well. Within two years, over 90% of Ethereum blocks were built via MEV-Boost, and the construction market calcified around a handful of players.

The 2025 numbers from relayscan.io tell the story bluntly:

  • Titan Builder: ~46.5% of blocks, ~$19.7M profit
  • Rsync Builder: ~15.6%
  • Flashbots: ~12.8%
  • Beaverbuild: ~9.4%

A Herfindahl-Hirschman Index reading near 3,892 places the builder market well beyond the U.S. Department of Justice's threshold of 1,800 for "highly concentrated." Titan's profit margin under exclusive order flow deals reportedly exceeds 17%, while Flashbots — which originally seeded the entire MEV-Boost ecosystem — barely breaks even on block building today.

That is the market ePBS aims to dismantle at the protocol level.

What EIP-7732 Actually Changes​

EIP-7732 is deceptively surgical. It is a consensus-layer-only upgrade that decouples execution validation from consensus validation, both logically and temporally. In plain terms, the proposer no longer needs to see the full block's execution payload before committing to it.

Here is the new flow:

  1. Builders assemble execution payloads off-chain and broadcast signed SignedExecutionPayloadBid commitments containing only a blockhash and a payment value.
  2. The proposer selects the highest bid and embeds the commitment in the beacon block — without seeing the transactions inside.
  3. A new subset of validators, the Payload Timeliness Committee (PTC), attests whether the builder revealed the committed payload on time with the correct blockhash.
  4. Execution validation is postponed until the next slot's beacon block validation.

The critical engineering insight is that the full execution payload no longer rides on the consensus critical path. Network propagation speeds up, validators shoulder less computational load per slot, and — the part every MEV researcher has been waiting for — the relay becomes redundant. The builder commits cryptographically; the protocol itself enforces the promise.

Why This Guts The Relay Business​

Today, relays exist because proposers cannot trust builders directly. A relay like Flashbots or Titan Relay holds the full block, verifies it, and only reveals it to the proposer after the proposer signs the header — preventing the proposer from stealing the builder's MEV.

ePBS makes that trust relationship native to the protocol. The PTC handles timeliness enforcement. The consensus rules handle payment. The entire middleware layer Flashbots built to coordinate block building — the most important piece of Ethereum infrastructure outside the client software itself — becomes economically unnecessary.

This is why the coindesk coverage framed Glamsterdam as a fight about MEV fairness, not just performance. The question is not whether MEV disappears. MEV is a mathematical consequence of ordered transactions with public mempools. The question is who captures it and on what terms.

The Censorship Math Changes Too​

The relay oligopoly did not just concentrate power; it concentrated compliance. At peak, roughly 72% of MEV-Boost blocks were classified as OFAC-compliant because the largest relays filtered sanctioned addresses. That number has since declined to around 30% of relayed blocks as non-censoring relays gained share, but the architecture still gives a handful of US-based companies veto power over which Ethereum transactions get proposed.

ePBS does not mandate censorship resistance. But by removing the relay bottleneck, it removes the natural enforcement point. Builders who censor now have to compete against builders who do not on raw auction price — and on a trustless bid-reveal market, price tends to win. Expect the OFAC-compliant share to drop further after Glamsterdam ships, simply because the easiest place to impose policy has been eliminated.

Jito, Base, and Three Ways To Price A Block​

Ethereum is not the first chain to confront MEV markets, and it is worth comparing ePBS against the two other models that dominate 2026.

Solana's Jito approach. Over 94% of Solana stake runs the Jito-Solana client. Tips flow directly to validators through an explicit auction — no relay, no builder-proposer split. MEV contributes 15-25% of total validator rewards, and the connection to stakers via JitoSOL is direct. The upside is transparency; the downside is that Solana's leader schedule concentrates MEV extraction windows in ways that still produce sandwich attacks on DEX traders.

Base's sequencer model. Coinbase operates the single sequencer on Base and captures sequencer revenue directly. There is no MEV auction to third parties because there are no third parties. This maximizes revenue capture for the L2 operator but sacrifices the decentralization story entirely — a tradeoff that works for Coinbase-scale balance sheets and nobody else.

Ethereum's ePBS. A trustless bid-reveal auction between builders and proposers, mediated by consensus. In theory this combines Jito's transparency with the credibly neutral distribution Ethereum's ideology requires. In practice, nobody knows yet whether builder concentration simply reasserts itself under new rules, or whether the removal of exclusive-order-flow agreements genuinely reopens the market.

The $500M Question For DeFi Users​

Researchers estimate DeFi users lose north of $500 million annually to sandwich attacks, frontrunning, and JIT liquidity extraction — with sandwich attacks alone responsible for 51% of MEV volume in 2025. EigenPhi's data from late 2025 found over 72,000 sandwich attacks targeting 35,000 victims on Ethereum in a single 30-day window. A single Uniswap v3 stablecoin swap in March 2025 saw $220,764 of USDC compressed into $5,271 of USDT — a 98% loss to the victim.

Does ePBS reduce this? Directly, no. The attack surface — public mempools plus arbitrary transaction ordering — remains. But ePBS reshapes the ecosystem around MEV protection:

  • Private mempool services like MEV-Blocker ($5B+ in protected transactions routed historically) and CowSwap's coincidence-of-wants batching retain their value, because the protocol still does not hide user intent.
  • Encrypted mempools like EIP-8105's "Universal Enshrined Encrypted Mempool" become the logical follow-on proposal, tackling the order visibility that ePBS leaves untouched.
  • SUAVE and decentralized sequencing remain relevant as application-layer MEV protection rather than infrastructure monopolies.

The short version: ePBS fixes who gets paid for ordering transactions, not whether users can be exploited through ordering. The second fight is just beginning.

What Builders Should Actually Watch​

Three signals will tell you whether ePBS delivers on its decentralization promise or quietly reproduces the old oligopoly:

  1. HHI after six months. If the builder HHI remains above 2,500 post-ePBS, the concentration problem was about economies of scale, not middleware, and no amount of protocol surgery will help. If it falls below 1,800, ePBS worked as advertised.

  2. Exclusive order flow agreements. Current builder margins depend on private deals with Uniswap, Banana Gun, and other high-value order flow sources. ePBS does not directly outlaw these, but it changes the leverage. Watch whether flagship integrations migrate to BuilderNet-style open consortia or stay exclusive.

  3. Non-censoring block share. Post-Glamsterdam, the relay-based censorship chokepoint is gone. If OFAC-compliance share stays above 50% anyway, it reveals that compliance pressure on Ethereum is structural rather than infrastructural.

The Infrastructure Reality Check​

Glamsterdam will reshape how Ethereum orders transactions, but it will not touch what most infrastructure providers actually do: run nodes, serve RPCs, index state. The block-building layer has always been a rarefied slice of the stack. For developers building on top of Ethereum, the practical impact of ePBS is indirect — slightly faster propagation, modestly more credible neutrality, and a likely shift in which MEV protection services matter most.

BlockEden.xyz provides enterprise-grade API infrastructure for Ethereum, Sui, Aptos, and 20+ other chains, with SLA-backed RPC endpoints that insulate your application from consensus-layer changes. Explore our API marketplace to build on infrastructure designed to outlast any single upgrade.

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