Regulated Validator Operations for MEV-Boost

introduction

COMPLIANCE ARCHITECTURE

Introduction

A technical guide for validators operating under legal mandates to censor at the relay level, covering configuration, operational risks, and resilience strategies.

Regulated and compliant validator operations within the MEV-Boost ecosystem require a deliberate, technically precise configuration to meet legal mandates such as OFAC sanctions compliance. This is achieved by curating a relay list that exclusively queries censoring relays—those that filter transactions from sanctioned addresses before delivering blocks to proposers. The primary operational mechanism is the -relays flag in the MEV-Boost sidecar, which must be restricted to a set of endpoints known to enforce a compliance policy, such as those operated by BloXroute (Regulated), Blocknative, and others that explicitly advertise OFAC-compliant filtering.

This operational posture introduces a distinct risk profile. By connecting only to a subset of relays, a validator sacrifices execution-layer reward optimization, as they are blind to blocks from non-censoring builders and relays that may contain higher MEV rewards. Furthermore, it creates a centralizing dependency on the uptime and honesty of a smaller relay set; an outage or performance degradation across compliant relays can directly lead to missed proposals. The -min-bid setting becomes a critical safeguard in this context, as it can force a fallback to local block building if the censored block value falls below a defined economic threshold, preventing the validator from proposing a low-value or empty block.

Institutions must treat this configuration not as a one-time setup but as a dynamic operational process. Relay policies, endpoints, and performance characteristics change. A robust compliance program requires continuous monitoring of relay uptime, latency, and the specific transaction-filtering logic applied, which may differ between relay operators. Chainscore Labs provides a compliance architecture review for institutions, analyzing the end-to-end relay selection strategy, fallback mechanisms, and monitoring stack to ensure that legal requirements are met without introducing unacceptable slashing risks or revenue degradation.

COMPLIANCE OPERATIONS

Quick Facts

A technical overview of the operational changes, risks, and actions required for validators to enforce transaction censorship at the relay level.

Area	What changes	Who is affected	Action
Relay Configuration	Validator must configure a censoring relay list, typically using the `-relays` flag to point exclusively to OFAC-compliant relays.	Validators, Staking Pools	Audit relay list configuration to ensure no non-compliant relays are accidentally included.
Block Building	Validator exclusively receives blocks from builders who submit to compliant relays, potentially reducing block value and missing non-censored blocks.	Validators, Staking Pools	Monitor `min-bid` and profit-switching logic; a lower block value is a direct cost of compliance.
Censorship Resistance	The validator's operational security model shifts from protocol liveness to legal liability; a misconfiguration can lead to proposing a non-compliant block.	Compliance Officers, Node Operators	Implement strict change control and monitoring for the relay configuration file to prevent unauthorized modifications.
Relay Liveness	The validator's uptime is now dependent on the liveness of a smaller, specific subset of relays. An outage of all compliant relays will force local block building.	Validators, Infrastructure Teams	Develop a fallback procedure that prioritizes local block building over failing over to a non-compliant relay to maintain liveness without violating policy.
Software Updates	A standard MEV-Boost or relay client update could reset or alter relay configurations, potentially introducing non-compliant relays.	DevOps, Node Operators	Integrate a relay-list integrity check into the deployment pipeline to validate the configuration post-update.
Monitoring and Alerting	Standard monitoring for relay health and profitability is insufficient; new alerts are needed for configuration drift and the availability of compliant relays.	SRE, Monitoring Teams	Create specific alerts for: 1) a change in the connected relay set, and 2) zero available compliant relays.
Slashing Risk	The risk of slashing is unchanged by the relay policy, but the risk of a compliance violation from proposing a non-censored block is introduced.	Risk Managers, Compliance Officers	Model a compliance violation as a new, high-severity operational risk with its own probability and impact assessment.

technical-context

REGULATED RELAY CONFIGURATION

Technical Mechanism of Censorship Compliance

How validators under legal mandates configure MEV-Boost to interact exclusively with OFAC-compliant relays, and the operational risks this introduces.

A validator operating under a legal mandate to comply with sanctions lists from the U.S. Office of Foreign Assets Control (OFAC) must ensure it does not propose blocks containing transactions linked to sanctioned addresses. In the MEV-Boost architecture, this compliance is technically enforced not by the validator client itself, but by restricting the validator's connection to a curated set of censoring relays. These relays, operated by entities like BloXroute (Regulated) and Agnostic, filter transactions against OFAC's Specially Designated Nationals (SDN) list before offering a block to the proposer. The validator's -relays flag in its MEV-Boost configuration becomes the single point of enforcement, creating a binary operational state: the validator is either connected to a censoring relay set and compliant, or it is not.

This configuration creates a direct dependency on the relay operator's internal compliance logic and its real-time synchronization with sanctions data. A validator has no way to independently audit the block body it signs; it only sees a blinded header. Therefore, the legal and technical liability for proposing a non-compliant block is delegated entirely to the relay's software and operational integrity. This introduces a critical risk: a bug in the relay's filtering logic, a delay in updating its sanctions list, or a relay operator's unilateral decision to alter its policy could cause the validator to unknowingly propose a non-compliant block, breaching its legal obligations. Furthermore, this practice directly contributes to builder centralization and systemic censorship at the protocol level, as builders who do not censor are excluded from the block-building market for these validators.

For institutional validators, a robust compliance architecture requires more than a static relay list. It demands continuous monitoring of relay behavior, including cross-referencing proposed blocks against sanctions lists using independent post-hoc analysis. Operators must also prepare for fallback scenarios where no compliant relay is available, which could force a choice between missing a slot and violating a legal mandate. Chainscore Labs provides a compliance architecture review for staking institutions, assessing the resilience of relay configurations, verifying monitoring and alerting systems for censorship compliance, and designing fallback procedures that balance legal obligations with operational uptime.

COMPLIANCE IMPACT ANALYSIS

Affected Actors and Systems

Institutional Validators

Institutions operating validators under legal mandates face direct operational impact. The primary requirement is configuring a censoring relay list that filters blocks containing transactions to sanctioned addresses.

Key actions:

Audit current relay list against OFAC SDN list compliance requirements
Implement relay-level filtering using compliant relays (e.g., BloXroute Regulated, Agnostic Gnosis)
Document compliance configuration for regulatory examinations
Monitor for missed slots caused by relay censorship reducing available block space

Risk factors:

Reduced block opportunities when compliant relays have lower builder participation
Potential APY reduction of 5-15% compared to non-censoring validators
Single-relay dependency risk if only one compliant relay is used

Chainscore offers a compliance architecture review to validate your relay configuration against regulatory requirements while maintaining operational resilience.

implementation-impact

COMPLIANCE AND RESILIENCE

Operational Impact and Architecture

The architectural and operational consequences of enforcing OFAC-compliant relay lists, including censorship risks, missed slot dynamics, and multi-relay fallback strategies.

Censorship-Enforced Relay Configuration

Validators implement compliance by constraining their MEV-Boost -relays flag to a subset of relays that filter transactions against sanction lists. This creates a deterministic censorship boundary at the relay level. Operators must verify that their chosen relays use the same regulatory filter list and update logic to avoid compliance gaps. A misconfiguration where one relay does not filter breaks the compliance posture and introduces legal risk.

EXPLORE

Missed Slot and Profit Degradation Risk

A censoring relay list reduces the pool of available builders and blocks. If all compliant relays fail to deliver a block in time, the validator will miss the slot or fall back to a locally built block, which typically yields lower rewards. Operators must model the expected APY reduction against the compliance requirement. Chainscore can simulate the profitability impact of a specific censoring relay set against historical mainnet data to quantify the revenue trade-off.

Multi-Relay Fallback Architecture

To balance compliance with uptime, validators should configure multiple censoring relays. MEV-Boost queries all relays in parallel and selects the highest-value valid header. If one compliant relay is slow or down, another can provide a block, preventing a missed slot without breaking the censorship policy. This requires careful testing of relay latency and reliability under your specific network topology.

Consensus Client Compatibility and Circuit Breakers

The --builder-circuit-breaker flag in clients like Lighthouse and Prysm allows validators to automatically fall back to local block building if MEV-Boost is unhealthy. In a regulated setup, this local block will not be censored, creating a compliance violation during fallback. Operators must either disable this feature or implement a custom sidecar proxy that enforces a local transaction filter before the execution client proposes the block.

Relay Monitoring and Compliance Drift Detection

A relay's censorship policy is an off-chain software configuration that can change without notice. A relay operator could accidentally or intentionally remove a filter, exposing the validator to non-compliant blocks. Institutional validators must implement continuous monitoring that audits the transaction content of blocks proposed through their relay set, alerting immediately if a sanctioned address appears in a proposed payload.

Chainscore Compliance Architecture Review

Chainscore Labs provides a targeted review for institutions that must operate validators under regulatory mandates. The engagement covers relay selection risk, circuit-breaker configuration, fallback transaction filtering, monitoring architecture, and a failure mode analysis that maps each component failure to its compliance and slashing outcome. The deliverable is a hardened reference architecture that satisfies legal requirements without sacrificing operational resilience.

OFAC AND REGULATORY COMPLIANCE RISK ASSESSMENT

Risk Matrix for Compliant Operations

Evaluates the operational, security, and revenue risks introduced by configuring validators to use a censoring relay list for regulatory compliance.

Risk Area	Failure Mode	Severity	Affected Actors	Mitigation and Action
Censorship Correlation	A supermajority of validators use the same compliance list, causing systemic transaction censorship and damaging Ethereum's credible neutrality.	High	Validators, Protocol Developers, Community	Monitor aggregate censorship metrics via relayscan.io. Diversify relay lists to include non-censoring relays where legally permissible. Chainscore can model censorship correlation risk for your specific jurisdiction.
Missed Slot Revenue	All compliant relays fail to deliver a block in time, and the validator has no non-censoring fallback, forcing a missed proposal and loss of MEV + priority fees.	High	Validators, Staking Pools	Configure a local execution client as a fallback builder. Set a competitive `min-bid` to reject unprofitable compliant blocks. Chainscore can audit your fallback and profit-switching configuration.
Builder Centralization	Only a small set of regulated, KYC'd builders are allowed on compliant relays, reducing competition and potentially lowering long-term block rewards.	Medium	Validators, Staking Pools	Track builder diversity on your chosen relays. Advocate for open, competitive builder markets within compliance frameworks. Chainscore provides builder concentration impact analysis.
Relay Operational Risk	A compliant relay experiences an outage or is decommissioned, and validators relying exclusively on it are exposed to missed slots until they update their configuration.	Medium	Validators, Staking Pools	Use multiple compliant relays for redundancy. Implement automated relay monitoring and alerting for liveness. Chainscore can design a resilient multi-relay compliance architecture.
Legal Precedent Risk	Using a specific compliance list is later deemed insufficient by regulators, or conversely, using a non-censoring relay is penalized, creating legal liability for the operator.	High	Validators, Custodians, Exchanges	Engage legal counsel to formally review relay selection policies. Document the technical rationale for compliance configurations. Chainscore offers a compliance architecture review to align technical implementation with legal guidance.
Inclusion List Incompatibility	A future Ethereum protocol upgrade mandates inclusion lists that conflict with relay-level censorship, forcing a choice between protocol non-compliance and regulatory non-compliance.	Critical	Validators, Client Teams, Protocol Developers	Participate in Ethereum governance and research forums (e.g., ethresear.ch) to advocate for designs that accommodate compliance needs. Chainscore can assess the impact of upcoming protocol changes on your compliance posture.
Data Availability and Privacy	A compliant relay's data handling practices are opaque, creating a risk that transaction metadata or validator IP information is leaked or mismanaged.	Low	Validators, Searchers	Review the data privacy policy and operational security of each relay used. Prefer relays with a proven track record and transparent operations. Chainscore can perform a relay operational security review.

REGULATED VALIDATOR OPERATIONS

Compliance Implementation Checklist

A technical checklist for validators required to operate under regulatory mandates, such as OFAC compliance. This guide focuses on the practical configuration of a censoring relay list, the associated operational risks, and the verification steps needed to ensure legal requirements are met without compromising validator resilience.

Formally define which relays are considered compliant for your jurisdiction. This is not a software setting but a governance decision.

What to check:

The specific legal or regulatory requirement (e.g., OFAC sanctions list).
Whether the mandate applies to the validator's own block production or extends to blocks built by external builders.
The list of relays that publicly enforce a censorship policy aligned with your requirements.

Why it matters: A written policy is the foundation for all technical configuration. It provides a defensible audit trail and ensures operational teams understand the boundary between a compliant block and a non-compliant one.

Readiness signal: An internal document exists that lists approved relays by URL, specifies the regulatory standard they meet, and defines the review cadence for this list.

resource-links

COMPLIANCE OPERATIONS

Source Resources and Monitoring

Use canonical software, sanctions data, relay disclosures, and independent telemetry to maintain an auditable MEV-Boost operating posture. Relay selection alone does not establish legal compliance; operators should validate requirements with qualified counsel and continuously test actual block-delivery behavior.

MEV-Boost Releases and Configuration

Track the official MEV-Boost repository for releases, configuration changes, security-relevant fixes, and relay connection behavior. Pin reviewed versions, verify release artifacts, and test upgrades against every supported consensus client before fleet-wide deployment. Record relay URLs, command-line flags, fee-recipient configuration, fallback behavior, and approval history as controlled configuration. A compliant relay list is only one layer: the validator must still preserve local block production when relays time out or return unusable payloads.

EXPLORE

Relay Implementation and Policy Verification

Review the Flashbots relay implementation to understand proposer registration, bid validation, block simulation, payload delivery, and database dependencies. Institutions should distinguish software capabilities from each operator's deployed filtering policy. Request current policy statements, filter scope, sanctions-data refresh procedures, jurisdiction, change-notification commitments, and incident contacts from every relay. Independently test observed delivery behavior because a relay's public label does not prove that every builder submission or transaction was screened under the institution's required standard.

EXPLORE

Builder API Compatibility

Monitor the Ethereum builder specifications for changes to proposer-builder separation interfaces, including validator registration, header retrieval, blinded-block submission, and fork-specific data structures. Interface changes can affect relay availability or cause failed proposals even when compliance controls remain unchanged. Maintain a compatibility matrix covering MEV-Boost, consensus clients, relays, and the active Ethereum fork. Stage schema or endpoint changes in pre-production and verify that local block-building fallback remains available under relay rejection, timeout, or malformed-response scenarios.

EXPLORE

OFAC Sanctions Source Monitoring

Use the U.S. Treasury's official sanctions search as a primary source when OFAC obligations apply. Compliance teams should define how list updates are ingested, normalized, reviewed, and propagated to relay or transaction-screening controls. Address matching alone may be insufficient for an institution's legal standard, while overbroad filtering can increase censorship and availability risk. Preserve source timestamps, matching logic, exceptions, approvals, and deployment evidence. Teams operating in other jurisdictions should maintain equivalent workflows for each applicable authority rather than treating OFAC data as universal.

EXPLORE

Relay Performance and Delivery Monitoring

Use RelayScan as an external observation source for relay and builder activity, but reconcile third-party data with validator-side logs and beacon-chain outcomes. Alert on relay timeouts, missing bids, late headers, payload-delivery failures, unexpected builder concentration, and sustained changes in relay participation. Segment results by region, client, relay, and validator cluster. Compliance-driven relay restrictions can reduce redundancy, so operators should measure missed-slot exposure and revenue effects while ensuring that profitability logic never silently bypasses an approved relay policy.

EXPLORE

Compliance Evidence and Exception Runbook

Maintain an internal evidence package covering approved relays, documented relay policies, sanctions-source versions, configuration hashes, change tickets, monitoring records, and proposal-level outcomes. Define escalation paths for policy drift, sanctions updates, relay outages, ambiguous matches, and emergency removal of a relay. The runbook should state whether local block production is permitted during a compliant-relay outage and which controls apply to locally sourced transactions. Periodically exercise the procedure with legal, compliance, security, and validator operations teams, then remediate gaps found during testing.

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COMPLIANCE OPERATIONS

Frequently Asked Questions

Technical and operational answers for validators implementing a regulated relay policy while managing the associated performance and security risks.

Compliance is enforced at the relay selection level within your MEV-Boost configuration. The primary method is to use the -relays flag to specify an explicit, static list of relays that enforce OFAC sanctions screening on the blocks they deliver.

Implementation Steps:

Identify Compliant Relays: Select relays that publicly commit to and verifiably enforce a compliance policy. Examples include the BloXroute Regulated Relay, Aestus, and Agnostic Gnosis.

Update MEV-Boost Configuration: Modify your MEV-Boost service file or container command to only include the chosen relay URLs.

bash
# Example: Static compliant relay list
mev-boost -relays "https://0x...@bloxroute.regulated.blxrbdn.com,https://0x...@aestus.live"

Disable Dynamic Relay Sources: Ensure you are not using a public relay list URL that could inject non-compliant relays into your configuration without notice.
Verify Configuration: After restarting, check the MEV-Boost logs or query the /eth/v1/builder/status endpoint to confirm the active relay set matches your intended compliant list.

Why it matters: A misconfiguration, such as accidentally including a non-censoring relay, can lead to your validator proposing a block containing transactions that violate sanctions, creating immediate legal exposure.

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Regulated and Compliant Validator Operations

Introduction

Quick Facts

Technical Mechanism of Censorship Compliance

Affected Actors and Systems

Institutional Validators