Citation

Ota, K., Rezzoli, D. “Mapping Public and Private JIT Liquidity Dynamics in Ethereum’s Builder Ecosystem.” University of Tokyo / PBS Foundation. (2026)

Core Contribution

First comprehensive empirical analysis of JIT (Just-In-Time) liquidity under PBS, covering both public mempool and private relay channels. Identifies 442,000 JIT bundles (Jan 2024 – Sep 2025), including ~52,700 private bundles.

What is JIT Liquidity?

JIT liquidity = ephemeral liquidity provision centered around a trade within a single block:

  • Mint: LP adds concentrated liquidity immediately before a swap
  • Swap: target transaction executes against the LP’s just-added position
  • Burn: LP removes liquidity immediately after the swap

This allows a “liquidity provider” to act like a market maker — providing liquidity only when a trade is incoming, capturing fees without holding inventory risk between blocks.

Key Empirical Findings

Scale and Concentration

  • 442,000 total JIT bundles (Jan 2024 – Sep 2025)
  • 52,700 private bundles (~11.9% of all JIT)
  • Among top builder-searcher pairs (>1% of total):
    • Public JIT: 90.07% of occurrences
    • Private JIT: 9.93% of occurrences

Private Channel Concentration

  • 100% of private bundles attributed to a single searcher: SCP
  • 78.04% of SCP’s private bundles route to Beaver builder
  • This represents extremely high concentration: one searcher, one builder relationship for private JIT

Public vs. Private Fee Dynamics

ChannelAvg total feesPass-through (price impact)Pass-through (fee income)
Public JITHigher~0.75 (strong, significant)~0.75 (strong, significant)
Private JITLower per bundle~0.32 (significantly weaker)Not significantly different

Interpretation: On public routes, both the price impact component and the fee income component are strongly associated with higher builder fees — competitive bidding for profitable opportunities. On private routes, only fee income strongly predicts fees; price impact is weakly transmitted, suggesting weaker bidding pressure or partial exclusivity reducing the need to bid aggressively.

Integrated pairs (known searcher-builder relationships) remit higher observed total fees conditional on realized profits — consistent with the exclusive order flow literature.

Detection Methodology

JIT window definition: Mint → Swap(s) → Burn in the same block and pool, same LP owner, Mint before Burn in transaction index order.

Public vs. private classification: using Flashbots Mempool Dumpster. If swap hash present in Dumpster → public. If none of the window hashes visible → private.

Implications

For MEV Economics

  • Private JIT is real but small relative to public JIT (~12%)
  • SCP→Beaver dominance in private JIT suggests a single integrated relationship captures most private JIT value
  • Weaker fee pass-through in private channels → JIT profit is partly captured outside the public fee market (off-chain arrangements or relationship rents)

For LP Returns and DEX Design

  • JIT liquidity providers behave as market makers, not traditional LPs
  • Their concentrated provision improves execution for large swaps but reduces fee income for traditional LPs
  • JIT is a form of informed liquidity provision that benefits searchers at the expense of passive LPs

For Block Building

  • JIT bundles paid to builders are smaller in private channels → private channel value is partly captured by the searcher or via off-chain payments
  • Builder selection by JIT searchers is highly concentrated: Beaver via BuilderNet captures dominant share

Connection to Existing Wiki

Key Sources

  • Mapping Public and Private JIT Liquidity Dynamics in Ethereum’s Builder Ecosystem (Ota, Rezzoli, 2026)