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MEV Builder Dominance: 5 Builders, 96.7% of Blocks

Why This Matters

MEV (Maximal Extractable Value) has been called Ethereum's "invisible tax." When a small number of builders dominate block construction, it creates:

• Censorship risks: Fewer entities can selectively exclude transactions
• Centralization pressure: Stakers are incentivized to use dominant builders for higher rewards
• Market fragility: Loss of any major builder could disrupt the MEV supply chain

Data & Methodology

Dataset: xatu ClickHouse mainnet (48h window)

Tables: mainnet.fct_block_mev_head, mainnet.fct_block_first_seen_by_node

Key Metrics

• MEV Block Percentage: ~0.55% of all blocks are MEV blocks (expected given slot/validator ratio)
• C4 Index: Share held by top 4 builders (avg: 55.3%)
• HHI: Sum of squared market shares × 10000 (avg: 2141)

Query: MEV vs Local Block Percentage

WITH mev_blocks AS (
    SELECT toStartOfHour(slot_start_date_time) AS hour, COUNT() AS mev_count
    FROM mainnet.fct_block_mev_head FINAL
    WHERE slot_start_date_time >= now() - INTERVAL 48 HOUR 
      AND value IS NOT NULL
    GROUP BY hour
),
all_blocks AS (
    SELECT toStartOfHour(slot_start_date_time) AS hour, COUNT() AS total_count
    FROM mainnet.fct_block_first_seen_by_node FINAL
    WHERE slot_start_date_time >= now() - INTERVAL 48 HOUR
    GROUP BY hour
)
SELECT a.hour, a.total_count, COALESCE(m.mev_count, 0) AS mev_count,
    COALESCE(m.mev_count, 0) * 100.0 / a.total_count AS mev_percentage
FROM all_blocks a LEFT JOIN mev_blocks m ON a.hour = m.hour
ORDER BY a.hour

Market Concentration Results

Top 5 builders control 96.7% of MEV blocks. The top builder maintains a dominant ~28% market share.

Implications

The MEV market concentration is concerning but not yet critical. The top builder's ~28% share means no single entity has unilateral censorship power, but coordinated action by the top 3-4 could.

For Ethereum's long-term health, the community should monitor:

• Builder diversity trends
• New builder entrants
• Potential cartel formation signals
• PBS (Proposer-Builder Separation) rollout effects

Caveats

• Builder pubkeys are pseudonymous—we don't know if "Builder A" represents a single entity or multiple cooperating entities
• Relay-level dynamics not captured—only on-chain data analyzed
• 48-hour window may miss longer-term trends
• Market share by block count may differ from share by extracted MEV value