Gas-backed pricing

fast-fill pricing has two layers:

1. The contracts enforce a simple signed fee curve: baseFee + timeFee.
2. The demo and relayers choose sane default signed values from factual inputs: gas benchmarks, live destination gas price, ETH/USD, and Circle CCTP fees.

This page documents the off-chain quote model used by the demo API and relayer profitability gates. The on-chain order fields are unchanged:

All token-denominated API fields are returned as decimal strings containing integer token base units ("1000000" means 1.000000 for USDC / USDt0).

Quote API

The demo form calls:

POST /api/bridge/pricing
content-type: application/json

Request:

{
  "bridgeType": 0,
  "token": "USDC",
  "srcChainId": 8453,
  "dstChainId": 42161,
  "amount": "1000000",
  "finality": 1000,
  "relayMint": true,
  "deliveryWindow": "60",
  "callbackGasLimit": "0"
}

Response:

{
  "params": {
    "maxFee": "...",
    "mintFee": "...",
    "baseFee": "...",
    "discountRate": "...",
    "deliveryWindow": "...",
    "outputAmount": "..."
  },
  "breakdown": {
    "gasPriceWei": "...",
    "ethUsd": "...",
    "fillGasUnits": "...",
    "fillGasFee": "...",
    "directSettleGasUnits": "...",
    "directSettleGasFee": "...",
    "executorGasUnits": "...",
    "executorGasFee": "...",
    "secondsSaved": "...",
    "targetTimeFee": "..."
  },
  "comparison": {
    "speed": "fast",
    "forwarding": true,
    "circleDirect": "...",
    "circleProtocolFee": "...",
    "circleForwardFee": "...",
    "circleClaimGas": "...",
    "circleExecGas": "...",
    "cctpDirectReceived": "...",
    "fastFillEstimated": "...",
    "savings": "..."
  }
}

comparison is present only for CCTP routes. It is a single apples-to-apples reference matching the request's settlement speed (finality) and forwarding choice (relayMint), not a matrix of every Circle option.

Inputs

The quote combines static gas budgets with live market data:

ETH/USD caching is controlled by:

Gas budgets

The pricing constants are:

The gas buffer is 25%. It gives room for gas price movement between quote and execution and leaves a small margin for relayers.

Gas is converted into USD-pegged token base units with:

ceil(gasUnits * gasPriceWei * ethUsd * 10^tokenDecimals * 1.25 / 1e18)

For example, with a 6-decimal USD token:

200,000 gas * 1,000,000 wei/gas * $3,000/ETH = 600 base units
buffered by 25% = 750 base units = $0.000750

This change intentionally scopes gas-to-token conversion to default USD-denominated routes (USDC and USDT0). Non-USD OFTs need an asset price source before they should be enabled with this model.

CCTP pricing

CCTP uses three fee buckets.

maxFee

maxFee is the CCTP source-side protocol fee cap.

For fast CCTP (finality = 1000), the quote fetches Circle's minimumFee bps and computes:

protocolFee = ceil(amount * minimumFeeBps / 10,000)
maxFee      = ceil(protocolFee * 1.20)

Circle can execute with feeExecuted <= maxFee. Any unspent CCTP fee is surplus that eventually flows back through settlement accounting.

For finalized CCTP (finality = 2000), the quote uses Circle's finalized-fee row. On supported routes this is normally zero.

mintFee

mintFee is non-zero only when Relay Mint is enabled.

mintFee = bufferedGasCost(350,000 + callbackGasLimit)

It pays whoever calls CctpExecutor.execute(message, attestation). This replaces a hand-configured flat mint fee with a route-specific gas quote.

baseFee

baseFee is the optimistic filler gas floor.

Relay Mint on:

baseFee = bufferedGasCost(59,495 + callbackGasLimit)

Relay Mint off:

baseFee = bufferedGasCost(59,495 + callbackGasLimit + 83,897)

Relay Mint off means the filler must cover both the optimistic fill and the direct CCTP settlement floor, so the direct settlement gas is included in baseFee.

The CCTP recipient output is:

outputAmount = amount - maxFee - mintFee

OFT pricing

OFT routes do not have CCTP maxFee or mintFee.

maxFee       = 0
mintFee      = 0
baseFee      = bufferedGasCost(59,495 + callbackGasLimit)
outputAmount = amount

LayerZero's native messaging fee remains separate and is displayed separately in the UI. The user is still paying LayerZero for delivery; fast-fill pricing only prices the optional speed-up.

Opportunity cost

The time premium prices the relayer's capital opportunity cost. The default assumption is 10% APR and a 15 second expected fill delay.

secondsSaved  = max(deliveryWindow - 15, 0)
targetTimeFee = ceil(outputAmount * 1,000 * secondsSaved / (10,000 * 31,536,000))

Where:

The quote then derives discountRate so the on-chain PricingLib fee curve reaches at least targetTimeFee at the expected 15 second fill time:

discountRate = ceil(targetTimeFee * 1e18 / (outputAmount * secondsSaved))

The derived rate is capped by the adapter's maxFeeRate behavior. This keeps the fee compatible with the same on-chain curve used by all orders.

For small demo transfers this often rounds up to exactly one token base unit. That is expected: 10% APR for a few minutes or seconds is extremely cheap.

CCTP comparison panel

The UI shows a CCTP-only comparison so users can compare fast-fill with using Circle directly. To keep it an apples-to-apples comparison, only the single Circle option that matches the user's chosen settlement speed and forwarding (Relay Mint) toggle is shown.

The reference reflects the full cost and number of steps of going direct, so it stays honest when fast-fill bundles work (claim + destination action) that the user would otherwise pay for separately:

circleExecGas matters because fast-fill runs any destination action (Aave deposit / Uniswap swap) atomically inside the fill — its gas is already in baseFee (via fillGasUnits). Going direct, the recipient must run that action as its own post-settlement transaction, paying its gas plus a fresh tx's intrinsic overhead; counting it keeps the comparison apples-to-apples.

The panel renders one Circle line (Circle fast/Circle slow, labelled with its steps — forwarding or self-claim, plus the action when set), the fast-fill estimate, a Cost line (signed saving and the percent cheaper/pricier vs Circle), and a Speed line (~1.5s typical fill vs the settlement window, with the fold-in that going direct also needs a separate action tx). cctpDirectReceived is also overlaid on the payout curve as an amber benchmark anchored at the settlement time.

The comparison is hidden for OFTs because LayerZero fees are always charged by the bridge; fast-fill only changes the speed/relayer premium.

Relayer enforcement

The quote is not only UI display. Relayers enforce it before spending capital.

The demo fallback relayer:

• Recomputes current pricing in submitGasless.
• Rejects signed gasless orders whose maxFee, mintFee, baseFee, or discountRate are below the current required quote.
• Recomputes the current gas-backed fill floor in fillOrder.
• Skips fills whose quoted feeToFiller is below the gas-backed floor plus RELAYER_MIN_FEE.

The Rust relayer:

• Uses the same gas conversion math beside price.rs.
• For routed CCTP fills, requires:

feeToFiller >= fillGasFloor + RELAYER_MIN_FEE

• For direct CCTP fills, requires:

feeToFiller >= fillGasFloor + directSettleGasFloor + RELAYER_MIN_FEE

• For OFT fills, requires:

feeToFiller >= fillGasFloor + RELAYER_MIN_FEE

The existing CctpExecutor.execute gas-estimate profitability gate remains in place for mint relaying; mintFee must still cover actual executor settlement profitability.

Why this is deliberately conservative

The model is designed to avoid hidden subsidies:

• Users see signed order values before submission.
• Relayers can reject stale or underpriced quotes.
• Gas prices are buffered but still derived from live destination data.
• Circle protocol and forwarding comparisons come from Circle's API, not static assumptions.
• The contract fields remain stable, so no Solidity migration is required.

If new non-USD tokens are enabled, the missing piece is a token/USD price source. Until then, gas floors should stay scoped to USD-denominated tokens.