Relayer(Filler)

Relayers (Fillers) are specialized entities that monitor cross-chain intent events and provide liquidity services by fulfilling user orders across multiple blockchain networks while maintaining substantial asset reserves and technical infrastructure necessary to execute complex operations through standardized settlement interfaces. In hybrid implementations combining ERC-7683 and ERC-4337, relayers perform dual functions:

• Asset Liquidity Provision: Execute cross-chain value transfers by providing upfront liquidity on destination chains through IDestinationSettler.fill() calls, earning fees from the spread between input and output amounts while managing capital risk across multiple networks.

• UserOperation Execution: Bundle and submit account abstraction transactions via EntryPoint.handleOps(), collecting gas fees from sponsored operations while ensuring validateUserOp() compliance and maintaining computational resources for ERC-7562 validation rules.

Relayer vs Bundler

Aspect	Cross-Chain Relayer (ERC-7683)	ERC-4337 Bundler	Hybrid Implementation
Primary Function	Execute cross-chain value transfers and provide liquidity	Bundle UserOperation and submit to EntryPoint	Execute cross-chain intents containing UserOperation
Validation Scope	Order profitability, token availability, deadline compliance	Opcode restrictions (ORIGIN, GASPRICE, BLOCKHASH blocked), storage access rules (SLOAD/SSTORE sandboxing), entity reputation tracking	Both profitability analysis AND ERC-7562 validation rules
Economic Model	Fee-based arbitrage between origin/destination chains	Gas fee collection from bundled operations	Cross-chain arbitrage + bundling fees
Risk Management	Capital risk from temporary liquidity provision	Computational DoS via validateUserOp() simulation limits	Both capital exposure AND computational validation costs
Mempool Management	Monitor cross-chain order pools via IDestinationSettler.fill()	Maintain UserOperation mempool per ERC-7562 rules	Dual mempool systems with cross-validation
Execution Timeline	Fill orders within fillDeadline constraints	Bundle operations for next block inclusion via handleOps()	Coordinate cross-chain fills with UserOp execution
Reputation System	Protocol-specific reputation mechanisms	Entity reputation per ERC-7562 (opsSeen/opsIncluded ratios, staking requirements)	Multi-layered reputation across protocols

Validation and Profit Assessment

1. Cross-Chain Fill Profitability Calculation

Relayers evaluate fill profitability using comprehensive cost-benefit analysis before committing capital:

Gross Revenue = Input Amount USD - Output Amount USD - LP Fee USD
Net Profit = Gross Revenue - Gas Cost USD - Capital Risk Premium
Profitable = Net Profit >= Minimum Relayer Fee USD

Gas cost estimation accounts for destination chain execution complexity:

Total Gas Cost USD = (Fill Gas Cost + Message Verification Cost) × Gas Token Price USD
Fill Gas Cost = estimateGas(fillCalldata) × gasPrice × gasMultiplier
Message Verification Cost = crossChainProof.length × DATA_GAS_COST

2. UserOperation Bundle Validation

bundlers implement multi-phase validation to ensure profitable and valid operation inclusion:

// Phase 1: Static validation
require(userOp.sender != address(0));
require(userOp.nonce == entryPoint.getNonce(userOp.sender, nonceKey));
require(userOp.callGasLimit >= MIN_CALL_GAS_LIMIT);
require(userOp.verificationGasLimit <= MAX_VERIFICATION_GAS);

Economic validation ensures sufficient funds for execution:

Required Prefund = Sum of (Gas Limit × Max Fee Per Gas) for:
  - Call Gas Limit
  - Verification Gas Limit  
  - Pre-verification Gas

3. Hybrid Operation Economics

Hybrid relayers must coordinate profitability across both cross-chain fills and UserOperation bundling:

Total Revenue = Cross-Chain Relayer Spread + Bundler Fee Collection
Total Gas Cost = Cross-Chain Fill Gas Cost + Bundle Submission Gas Cost
Hybrid Profitable = Total Revenue >= Total Gas Cost + Minimum Profit Margin

Validation synchronization ensures UserOperation validity persists across cross-chain execution delays:

// Nonce validation with time buffer
uint256 currentNonce = entryPoint.getNonce(userOp.sender, nonceKey);
require(userOp.nonce == currentNonce);
require(block.timestamp + maxCrossChainDelay <= userOp.validUntil);

Bundle gas limit calculation incorporates cross-chain coordination overhead:

Base Gas Per UserOp = Verification Gas + Call Gas + Pre-verification Gas + Cross-Chain Overhead
Total Bundle Gas = (Base Gas Per UserOp × Number of UserOps) + Bundle Overhead Gas
Bundle Valid = Total Bundle Gas ≤ Block Gas Limit × MAX_BUNDLE_GAS_RATIO