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arxiv: 2605.22667 · v2 · pith:RFFJLXAMnew · submitted 2026-05-21 · 💻 cs.GT · q-fin.TR

Imperfect Commitment in Maximal Extractable Value Auctions

Aleksei Adadurov , Sergey Barseghyan , Anton Chtepine , Antero Eloranta , Andrei Sebyakin , Arsenii Valitov This is my paper

Pith reviewed 2026-05-22 04:01 UTC · model grok-4.3

classification 💻 cs.GT q-fin.TR
keywords MEV auctionsimperfect commitmentblock builderssearchersEthereumdefectionarbitragesandwich opportunities
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The pith

Imperfect commitment allows Ethereum block builders to capture additional surplus from MEV opportunities after seeing bids.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper studies how block builders in MEV auctions can defect after observing searcher bids and bundles, since the protocol does not force them to honor the outcome. Builders are modeled as defecting with fixed probability ε and then replicating a type-specific fraction γ(τ) of the winning opportunity. Searchers anticipate this behavior and choose between a risky first-price bid or a safe deterrence bid that removes the profit from defection. The resulting equilibrium bidding is piecewise and the cost of imperfect commitment rises with both replicability and competition intensity. Data from the libmev dataset shows clear heterogeneity: sandwich opportunities are already highly competitive with little exposed surplus, while naked arbitrage and liquidations leave substantially more value open to builder defection.

Core claim

The equilibrium in these auctions with imperfect commitment produces a piecewise outcome in which the cost depends jointly on replicability γ(τ) and competition; empirical decomposition of observed auction revenue against the surplus a defecting builder could capture reveals sharp heterogeneity across MEV types, with sandwiches showing high competition and low exposed surplus while arbitrage and liquidations show the opposite.

What carries the argument

The defection model in which a builder defects with probability ε and replicates a type-specific fraction γ(τ) of the winning MEV opportunity, with searchers choosing between risky first-price bids and safe deterrence bids.

If this is right

  • The cost of imperfect commitment depends jointly on replicability and competition.
  • Sandwich opportunities are already highly competitive with minimal exposed surplus.
  • Naked arbitrage and liquidations leave substantially more surplus exposed to builder defection.
  • Credible MEV auctions require constraints on the builder's ability to use observed bid and payload information ex post.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Hiding bid or payload details from builders until after the block is built could lower effective defection incentives.
  • Comparing auction outcomes before and after any information-hiding rules would test whether the exposed surplus shrinks.
  • Allowing the defection probability to vary with opportunity size might sharpen the predicted heterogeneity across types.

Load-bearing premise

Builders defect with a fixed probability ε and replicate a type-specific fraction γ(τ) of the opportunity upon defection, and searchers correctly anticipate this when choosing between risky and safe bids.

What would settle it

Direct measurement of actual builder defection rates together with a check of whether the observed revenue decomposition matches the predicted surplus exposure for each MEV type.

Figures

Figures reproduced from arXiv: 2605.22667 by Aleksei Adadurov, Andrei Sebyakin, Antero Eloranta, Anton Chtepine, Arsenii Valitov, Sergey Barseghyan.

Figure 1
Figure 1. Figure 1: FIG. 1: Timing of the game [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2: Bribe percentage vs extracted value by MEV [PITH_FULL_IMAGE:figures/full_fig_p006_2.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4: Bergemann disclosure benchmark by effective [PITH_FULL_IMAGE:figures/full_fig_p007_4.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3: Auction revenue (blue) vs foregone frontrun [PITH_FULL_IMAGE:figures/full_fig_p007_3.png] view at source ↗
read the original abstract

Ethereum block builders run sealed auctions among searchers, but nothing in the protocol forces a builder to honor the auction outcome after observing submitted bundles. This paper studies the commitment problem. We model a builder who defects with probability $\varepsilon$ and, upon defection, replicates a type-specific fraction $\gamma(\tau)$ of the winning MEV opportunity. Searchers anticipate this behavior and choose between a risky first-price bid and a safe deterrence bid that makes frontrunning unprofitable. The resulting equilibrium is piecewise, with the cost of imperfect commitment depending jointly on replicability and competition. Using the libMEV dataset, we estimate $\gamma(\tau)$ from right-tail bribe plateaus and decompose observed auction revenue against the surplus a defecting builder could capture. The results show sharp heterogeneity across MEV types: sandwich opportunities are already highly competitive, while naked arbitrage and liquidations leave substantially more surplus exposed to builder defection. Credible MEV auctions, therefore, require not only an auction format, but also constraints on the builder's ability to use observed bid and payload information ex post.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The paper models imperfect commitment in MEV auctions on Ethereum, where a builder defects with fixed probability ε and, upon defection, replicates a type-specific fraction γ(τ) of the winning opportunity. Searchers anticipate this and select between a risky first-price bid and a safe deterrence bid. The resulting equilibrium is piecewise and depends on replicability and competition. Using the libmev dataset, the authors estimate γ(τ) from right-tail bribe plateaus, decompose observed auction revenue into surplus exposed to defection, and report sharp heterogeneity: sandwich opportunities are already highly competitive while naked arbitrage and liquidations leave substantially more surplus exposed.

Significance. If the identification of γ(τ) holds, the results demonstrate that auction formats alone are insufficient for credible MEV extraction and that ex-post constraints on builder information use are required. The theoretical equilibrium derivation provides a clean framework for analyzing commitment in repeated auctions with private information, and the data-driven decomposition offers a novel empirical lens on MEV-type heterogeneity.

major comments (2)
  1. [§5] §5 (Estimation of γ(τ)): The identification strategy locates right-tail bribe plateaus in the libmev data and interprets them as the replicable fraction γ(τ) a defecting builder can capture. This assumption is load-bearing for the heterogeneity claims, yet the paper does not provide robustness checks against alternatives such as equilibrium bid shading under varying searcher counts or intrinsic shapes of MEV profit functions (e.g., sandwich saturation). If plateaus arise from these factors instead, the subsequent decomposition of revenue into “surplus exposed to defection” misattributes differences across MEV types.
  2. [§6] §6 (Decomposition results): The reported surplus-exposure figures for each MEV type are constructed by subtracting a quantity that depends on the fitted γ(τ) estimated from the same auction data. This creates a circularity risk between the parameter and the heterogeneity conclusions; the paper should clarify whether the decomposition uses out-of-sample validation or alternative identification to break the dependence.
minor comments (2)
  1. [§3] Notation for the safe deterrence bid and the piecewise equilibrium thresholds could be clarified with an explicit table summarizing the four regimes.
  2. [§6] Figure 4 (or equivalent revenue decomposition plot): axis labels and legend entries should explicitly state that the exposed-surplus bars are computed using the estimated γ(τ) rather than raw data.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments on the identification strategy for γ(τ) and the potential circularity in our decomposition. We address each point below and outline revisions to strengthen the empirical sections.

read point-by-point responses

  1. Referee: §5 (Estimation of γ(τ)): The identification strategy locates right-tail bribe plateaus in the libmev data and interprets them as the replicable fraction γ(τ) a defecting builder can capture. This assumption is load-bearing for the heterogeneity claims, yet the paper does not provide robustness checks against alternatives such as equilibrium bid shading under varying searcher counts or intrinsic shapes of MEV profit functions (e.g., sandwich saturation). If plateaus arise from these factors instead, the subsequent decomposition of revenue into “surplus exposed to defection” misattributes differences across MEV types.

    Authors: We appreciate the referee's point on the load-bearing nature of the plateau interpretation. Our model predicts that right-tail stabilization occurs precisely when additional bidding no longer offsets the expected loss from replication, which aligns with the observed flat tails across opportunity sizes. While we acknowledge that searcher count variation or saturation could contribute, the theoretical framework distinguishes replicability-driven plateaus from pure shading because the latter would not produce type-specific heterogeneity consistent with the data. In revision we will add explicit robustness checks, including controls for searcher participation and comparisons of profit-function curvature across MEV types, to isolate the replicability channel. revision: partial

  2. Referee: §6 (Decomposition results): The reported surplus-exposure figures for each MEV type are constructed by subtracting a quantity that depends on the fitted γ(τ) estimated from the same auction data. This creates a circularity risk between the parameter and the heterogeneity conclusions; the paper should clarify whether the decomposition uses out-of-sample validation or alternative identification to break the dependence.

    Authors: We agree there is a dependence risk when γ(τ) and the decomposition draw from the same observations. To break this, the revised manuscript will implement a split-sample procedure: γ(τ) will be estimated on one partition of the data (by time or MEV subtype) and applied to the held-out partition for the surplus-exposure calculations. We will also report the resulting heterogeneity under this out-of-sample approach and discuss remaining limitations of the identification. revision: yes

Circularity Check

1 steps flagged

Revenue decomposition and MEV-type heterogeneity rest on γ(τ) fitted from the same libmev bribe data

specific steps
  1. fitted input called prediction [Abstract]
    "Using the libmev dataset, we estimate γ(τ) from right-tail bribe plateaus and decompose observed auction revenue against the surplus a defecting builder could capture. The results show sharp heterogeneity across MEV types: sandwich opportunities are already highly competitive, while naked arbitrage and liquidations leave substantially more surplus exposed to builder defection."

    γ(τ) is fitted from right-tail plateaus in the libmev data; the surplus a defecting builder could capture is then defined using that fitted γ(τ). The decomposition of observed revenue into exposed surplus therefore uses the same data-derived parameter, so the reported type-specific heterogeneity is statistically tied to the estimation procedure rather than an independent prediction or external benchmark.

full rationale

The paper estimates the replicability parameter γ(τ) directly from right-tail bribe plateaus observed in the libmev dataset for each MEV type τ. It then defines the surplus a defecting builder could capture in terms of this same γ(τ) and decomposes observed auction revenue against that quantity to produce the headline heterogeneity result (sandwiches competitive, arbitrage and liquidations more exposed). Because the exposed-surplus metric is constructed from the fitted γ values drawn from the identical data, differences across types are partly determined by the estimation step itself rather than emerging independently from raw revenue patterns. This matches the fitted-input-called-prediction pattern and raises the circularity score to 6 while leaving room for independent content in the equilibrium model and auction-format conclusions.

Axiom & Free-Parameter Ledger

2 free parameters · 1 axioms · 0 invented entities

The central claim rests on a behavioral model of builder defection and searcher anticipation plus empirical extraction of replicability from observed bids; these are not derived from first principles but introduced to match the institutional setting.

free parameters (2)
  • ε
    Probability that a builder defects after observing the winning bid; introduced as a modeling parameter without independent calibration shown in abstract.
  • γ(τ)
    Type-specific fraction of MEV opportunity replicable by a defecting builder; estimated from right-tail bribe plateaus in the libmev dataset.
axioms (1)
  • domain assumption Searchers correctly anticipate the builder's defection probability and replicability when choosing bids.
    Invoked to derive the piecewise equilibrium between risky first-price and safe deterrence bids.

pith-pipeline@v0.9.0 · 5745 in / 1346 out tokens · 53421 ms · 2026-05-22T04:01:28.760695+00:00 · methodology

discussion (0)

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