Summary

The MEV supply chain transforms raw transaction flow into validated blocks through four specialized roles: searchers extract MEV opportunities, builders assemble maximum-value blocks, relays act as trusted escrow between builders and validators, and validators propose the highest-value block they receive. Each actor has distinct incentives, competitive dynamics, and concentration risks.

1. Searchers

Role: Identify and capture MEV opportunities by submitting bundles to builders.

What they do:

  • Monitor public and private mempools for profitable opportunities
  • Construct transaction sequences (bundles) that extract value from pending transactions
  • Submit bundles directly to builder endpoints (not the public mempool)
  • Bid priority fees to ensure their bundles are included

Types of MEV they capture:

TypeMechanismValue (2026)
CEX-DEX arbPrice difference between centralized and on-chain venuesLargest
AMM arbPrice differences between on-chain DEXsSecond
LiquidationsUndercollateralized positions seized at discountThird
BackrunningExtract residual value after large tradesSignificant
SandwichingFront+backrun user trades (controversial)Overstated; ~0.37 bps median impact

Concentration: The top 1% of transactions account for ~68% of MEV revenue. CEX-DEX arbitrage in particular requires exchange API access, fast connectivity, and capital — creating barriers that concentrate this category among sophisticated, well-capitalized firms.

Searcher-builder relationships: Some searchers operate exclusively with specific builders, trading off competition for guaranteed inclusion and favorable split terms. Others submit to many builders competitively.

2. Block Builders

Role: Assemble the most valuable possible block from available transactions and bundles.

What they do:

  • Receive transactions from public mempool, private OFA flows, and searcher bundles
  • Sort and arrange transactions to maximize total block value (base fees + tips + MEV)
  • Submit competitive bids to relays with the assembled block
  • Operate with millisecond-level latency sensitivity (timing games)

Market structure (2026):

BuilderMarket shareCompetitive advantage
Titan Builder~47.6%Exclusive OFA partnerships; large searcher network
BuilderNet~26.0%TEE-based shared building; multi-operator resilience
Others~26.4%Niche flow, geographic coverage, specialization

Economics: Builders profit from the spread between what they bid to validators and the total block value they capture. This spread is positive only when they have access to flow unavailable to competing builders.

Technology stack: Sophisticated simulation engines (often multiple millisecond simulation of complex EVM transactions), co-location with relays, private peering networks, CEX API integrations for CEX-DEX arb.

3. Relays

Role: Trusted escrow between builders and validators in MEV-Boost.

What they do:

  • Receive full block bodies from builders
  • Verify blocks are valid (simulating the full block against current state)
  • Hold the block body; give the proposer only the block header and bid value
  • Release the full block body to the network after the proposer has committed to the header

Current relays:

  • Flashbots, bloXroute, Ultra Sound, Titan, Aestus, manifold
  • All US/EU-based → disadvantages validators in Asia (~120ms additional round-trip)
  • No relay in Asia, Africa, or South America as of 2026

Economics: No sustainable business model. Bear significant infrastructure costs (global presence, fast simulation, 99.9%+ uptime requirement) but cannot charge builders without losing volume to competing free relays. Most relays are subsidized by parent organizations.

Bid adjustment: Relays can and do adjust builder bids (~5% of slots, ~2% of value). This is an unresolved trust issue.

Post-ePBS (Glamsterdam): Relays lose their trusted escrow role. The commit-reveal happens at the protocol level; builders post bonds rather than trusting relays. Relays may continue as optional coordination services.

4. Validators (Proposers)

Role: Propose the highest-value block for their assigned slot.

What they do:

  • Receive block headers + bid values from relays via MEV-Boost
  • Select the highest-value bid
  • Sign the selected block header and broadcast it
  • Receive payment (priority fees + MEV share) from the chosen builder

Revenue components:

  • Base fees (burned, not received directly)
  • Priority fees (100% to validator)
  • MEV-Boost bid (builder’s winning bid amount)

MEV-Boost adoption: >90% of validators use MEV-Boost; pure local building is ~60% less valuable.

Geographic distribution (Lido Q4/2025):

  • Europe: 60% (Germany alone: 20.4%)
  • North America: 18.6%
  • Asia-Pacific: 17.3% (Australia 5.1%, Singapore 5.0%)
  • South America: 1.7%, Africa: 2.1%

5. OFA Providers (Intermediaries)

Role: Aggregate user transactions and auction backrun rights to searchers.

Key examples: Flashbots Protect, MEV Blocker, CoW Protocol
User benefit: protection from frontrunning + rebate on backrun value
Builder dependency: OFA providers route to specific builders → amplifies builder concentration

6. Wallets and DeFi Interfaces

Role: User-facing layer that controls transaction signing, routing, and broadcasting.

  • Control where >95% of retail transactions go (most users use defaults)
  • Have enormous leverage: shifting OFA partnerships can move billions in flow
  • May receive kickbacks from OFA providers or builders (regulatory scrutiny increasing)
  • Regulatory analysis (Flashbots, Apr 2026) examines whether this constitutes broker-dealer activity

Value Flow (Simplified)

User transaction value
    ↓
Builder extracts MEV surplus (via searchers)
    ↓
Builder bids to relay (max: total extracted value - profit margin)
    ↓
Proposer receives bid (net of relay fees)
    ↓
ETH staking yield for validator operators
    ↓
Fraction returned to stakers (Lido, Rocket Pool, etc.)

Key Tensions

  1. Concentration vs. resilience: current builder concentration (~74% in 2 builders) is efficient for MEV extraction but fragile and censorship-prone
  2. Relay trust: the trusted relay model is a centralized point of failure; ePBS addresses this
  3. OFA value capture: who should capture backrun value — the builder, the searcher, or the user (via rebate)?
  4. Geographic equity: relay and builder concentration in US/EU creates structural income inequality for non-Western validators

JIT Liquidity as a Specialized Searcher Strategy

Just-In-Time (JIT) liquidity providers are a specific searcher type who provide concentrated LP positions around large swaps:

  • Mint liquidity → swap executes → Burn liquidity, all within one block
  • 442,000 JIT bundles identified on Uniswap v3 mainnet, Jan 2024 – Sep 2025 (Ota, Rezzoli, 2026)
  • 52,700 private bundles (~12% of all JIT): concentrated in single searcher-builder relationship
  • SCP → Beaver: 100% of private JIT bundles are from searcher SCP; 78% route to Beaver builder
  • Public JIT has higher fees and stronger profit-to-fee pass-through (0.75) than private JIT (0.32 for price impact component)

This extreme concentration in private JIT confirms the exclusive order flow flywheel: a single integrated searcher-builder pair captures the most valuable JIT opportunities.

Key Sources

  • Three Years of PBS (Dec 2025) — structural gaps; actor landscape
  • Economics Align the Incentives (2026) — flywheel; relay bid adjustment; relay economics
  • Decentralized Building: wat do? (Flashbots, Feb 2026) — Phase 0–3 framing; actor roles
  • Ethereum’s Geographic Blind Spot (Four Pillars, Mar 2026) — validator distribution; relay geographic gap
  • Mapping Public and Private JIT Liquidity (Ota, Rezzoli, 2026) — JIT concentration; SCP→Beaver private channel; pass-through analysis