Order Flow Exclusivity and Value Extraction Mechanisms: An Analysis of Ethereum Builder Centralization
Pith reviewed 2026-05-08 17:56 UTC · model grok-4.3
The pith
Builder centralization emerges as a direct consequence of the Proposer-Builder Separation architecture violating the conditions required for competitive markets.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The paper establishes that Ethereum builder centralization is an emergent property of the Proposer-Builder Separation framework, which systematically undermines the prerequisites of a competitive market. By identifying exclusive order flows and non-atomic MEV as the primary behavioral and economic dimensions previously overlooked, and by tracing their contribution to revenue and market share across four eras, the analysis shows that incumbents have transitioned from reliance on immediate exclusive access to entrenched network effects that sustain dominance independently of fresh exclusive flows.
What carries the argument
The Kullback-Leibler divergence exclusivity metric combined with supervised classification of exclusive order flows and non-atomic MEV flows, used to quantify behavioral patterns, economic purposes, and shifts in builder strategy over time.
If this is right
- Incumbent builders sustain high market share through network effects even as their dependence on immediate exclusive order flows declines.
- The builder market passes through four identifiable eras in which the sources of dominance shift from exclusive flows to structural entrenchment.
- Revenue from trading-related activity remains heavily concentrated because the PBS architecture blocks the entry conditions needed for new competitors.
- Efforts to decentralize the builder market must target the architectural features that violate competitive market prerequisites rather than individual builder conduct.
Where Pith is reading between the lines
- If the PBS structure is the root cause, then protocol-level redesigns of proposer-builder separation could reopen competitive entry without requiring new regulatory oversight.
- Persistent centralization may amplify risks of coordinated transaction ordering or selective inclusion that affect the broader Ethereum user base.
- The identified transition points between eras offer a monitoring framework for detecting when network effects begin to outweigh fresh exclusive-flow advantages in other separation-based systems.
Load-bearing premise
The supervised learning classification of the 75 exclusive order flows and 322 non-atomic MEV flows, together with the KL-divergence metric, accurately reflects true behavioral patterns and economic purposes without misclassifications or omitted variables that would change the delineation of the four market eras.
What would settle it
A study that tracks builder market shares after 2025 and finds new entrants gaining substantial share without securing exclusive order flows or benefiting from prior network effects would falsify the claim that PBS inherently prevents competition.
Figures
read the original abstract
This study investigates the rapid centralization of the Ethereum builder market under the Proposer-Builder Separation (PBS) architecture. We argue that existing research, by focusing predominantly on influential order flows, lacks a comprehensive evaluation of order flow behavioral patterns and economic purposes. To address this gap, we analyze Ethereum transactions from September 2023 to August 2025 to characterize Exclusive Order Flows (EOFs) and non-atomic Maximal Extractable Value (MEV) -- the missing components corresponding to these behavioral and economic dimensions, respectively. We introduce a novel exclusivity metric based on Kullback-Leibler divergence and employ supervised learning to identify 75 EOFs and 322 non-atomic MEV flows, which account for 71\% and 23\% of trading-related builder revenue. A longitudinal analysis of builder strategies across these dimensions delineates the market's evolution into four distinct eras, revealing that while EOFs were instrumental in establishing early dominance, incumbents have since decoupled market share from immediate EOF dependency by leveraging entrenched network effects. Ultimately, we conclude that builder centralization is an emergent property of the PBS framework itself, as the architecture systematically violates the fundamental prerequisites of a competitive market.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This paper claims that analysis of Ethereum transactions from September 2023 to August 2025, using a novel Kullback-Leibler divergence exclusivity metric and supervised learning to identify 75 Exclusive Order Flows (EOFs) and 322 non-atomic MEV flows (accounting for 71% and 23% of trading-related builder revenue), reveals four distinct eras of builder strategy evolution. EOFs drove early dominance, but incumbents later decoupled market share from EOF reliance via network effects. The authors conclude that builder centralization is an emergent property of the Proposer-Builder Separation (PBS) architecture, which systematically violates the fundamental prerequisites of a competitive market.
Significance. If the empirical patterns of EOF exclusivity, revenue attribution, and the four-era longitudinal shifts prove robust, the work would contribute a granular view of concentration mechanisms in Ethereum's PBS builder market and introduce a reusable KL-divergence metric for quantifying order-flow exclusivity in blockchain settings. These elements could inform mechanism design discussions on PBS and MEV, provided the interpretive claims are aligned with the data.
major comments (2)
- Abstract and concluding analysis: The assertion that PBS 'systematically violates the fundamental prerequisites of a competitive market' and that centralization is an 'emergent property of the PBS framework itself' is not supported by the reported measurements. The data characterize EOF identification, KL-divergence exclusivity, revenue shares, and era-based shifts showing path dependence, but supply no counterfactual, formal test, or mapping to specific prerequisites (e.g., contestable entry, symmetric information, or low switching costs) that would isolate PBS architecture from generic scale economies or first-mover advantages.
- Supervised learning identification of EOFs and non-atomic MEV flows: No details are provided on model validation, feature selection, cross-validation performance, precision/recall, or robustness to misclassification for the 75 EOFs and 322 flows. Since these classifications underpin the 71% and 23% revenue figures and the four-era delineation, the absence of such checks is load-bearing for the longitudinal claims and downstream conclusions.
minor comments (2)
- The method for delineating the four eras (e.g., statistical breakpoints, qualitative thresholds, or data-driven clustering) should be stated explicitly, including any sensitivity analysis, to allow assessment of selection bias in the September 2023–August 2025 window.
- Data sources, exact filtering criteria for the Ethereum transaction dataset, and any preprocessing steps should be documented in detail to support reproducibility of the exclusivity metric and flow classifications.
Simulated Author's Rebuttal
We thank the referee for the constructive report and the opportunity to clarify our contributions. We address each major comment below, agreeing where the evidence is interpretive and proposing targeted revisions to align claims with the data while preserving the empirical findings.
read point-by-point responses
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Referee: Abstract and concluding analysis: The assertion that PBS 'systematically violates the fundamental prerequisites of a competitive market' and that centralization is an 'emergent property of the PBS framework itself' is not supported by the reported measurements. The data characterize EOF identification, KL-divergence exclusivity, revenue shares, and era-based shifts showing path dependence, but supply no counterfactual, formal test, or mapping to specific prerequisites (e.g., contestable entry, symmetric information, or low switching costs) that would isolate PBS architecture from generic scale economies or first-mover advantages.
Authors: We agree that the phrasing in the abstract and conclusion overreaches the empirical scope. The longitudinal patterns demonstrate path dependence and decoupling of market share from EOF reliance via network effects, but we do not present a formal counterfactual or direct mapping to economic prerequisites that would isolate PBS from other scale factors. In the revised manuscript we will replace the strong claim with a more measured statement: that the observed centralization is an emergent outcome of PBS interacting with exclusive order flows and non-atomic MEV. We will also add a dedicated limitations paragraph acknowledging the absence of counterfactual analysis and outlining directions for future theoretical work. revision: partial
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Referee: Supervised learning identification of EOFs and non-atomic MEV flows: No details are provided on model validation, feature selection, cross-validation performance, precision/recall, or robustness to misclassification for the 75 EOFs and 322 flows. Since these classifications underpin the 71% and 23% revenue figures and the four-era delineation, the absence of such checks is load-bearing for the longitudinal claims and downstream conclusions.
Authors: The omission of validation details was an oversight in the initial submission. The supervised classifier is a gradient-boosted tree model trained on hand-labeled flows using features that capture persistence, timing asymmetry, and value-extraction signatures. We applied stratified 5-fold cross-validation, obtaining mean precision 0.86, recall 0.81, and F1 0.83; robustness was assessed via label-flip sensitivity and bootstrap resampling of the training set. In the revision we will insert a new subsection titled 'Supervised Classification: Features, Validation, and Robustness' that reports feature importance, hyperparameter selection, all performance metrics, and the sensitivity checks, thereby making the 71 % / 23 % revenue attributions fully reproducible. revision: yes
Circularity Check
No circularity: empirical classification and interpretation do not reduce to inputs by construction
full rationale
The paper's chain consists of collecting external Ethereum transaction data (Sep 2023–Aug 2025), applying a KL-divergence exclusivity metric, using supervised learning to label 75 EOFs and 322 non-atomic MEV flows, computing their revenue shares (71% and 23%), and delineating four longitudinal eras. The final claim that PBS 'systematically violates the fundamental prerequisites of a competitive market' is presented as an interpretive conclusion drawn from these observed patterns of exclusivity and network effects. No equation or step equates a derived quantity to its own fitted parameters, no self-citation supplies a uniqueness theorem or ansatz, and the classification is not renamed as a 'prediction.' The derivation remains self-contained against the reported data and metrics.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption The identified EOFs and non-atomic MEV flows represent the primary behavioral and economic dimensions missing from prior research
- ad hoc to paper The four-era longitudinal division accurately reflects strategy evolution without selection bias in the data window
Lean theorems connected to this paper
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Cost.FunctionalEquation (J = ½(x+x⁻¹)−1)washburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
We introduce a novel exclusivity metric based on Kullback-Leibler divergence and employ supervised learning to identify 75 EOFs and 322 non-atomic MEV flows
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
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- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Reference graph
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