Suggested Fees API (Legacy / Advanced)

Use the /suggested-fees API when you control your own swap infrastructure and only need Across for the bridge leg. This is the lower-level path: you construct depositV3 calls manually.

For most integrations, use the Swap API (/swap/approval).

When to use this API

You have your own DEX aggregator and only need bridge fee quotes.
You want bridgeable-to-bridgeable transfers (same asset across chains).
You need fine-grained control over depositV3 call construction.

GET /suggested-fees

Returns suggested fees based on inputToken + outputToken, originChainId, destinationChainId, and amount. Also includes data used to compute the fees.

Required parameters

Parameter	Description
`inputToken`	Token address on origin chain (use wrapped token for native assets, e.g., WETH)
`outputToken`	Token address on destination chain (use wrapped token for native assets, e.g., WETH)
`originChainId`	Origin chain ID
`destinationChainId`	Destination chain ID
`amount`	Amount in token native decimals (USDC 1e6, WETH 1e18)

Optional parameters

Parameter	Description
`recipient`	Recipient of the deposit (EOA or contract). If this is an EOA and `message` is set, the API returns an error
`message`	Calldata for contract recipients; passed to `handleAcrossMessage()` on the recipient
`relayer`	Override the relayer used to simulate `fillRelay()` for gas estimation
`timestamp`	Quote timestamp used to compute LP fees. Must be close to current time and <= current mainnet block timestamp. Defaults to latest mainnet block timestamp

Key response fields

totalRelayFee (pct + total)
relayerCapitalFee (pct + total)
relayerGasFee (pct + total)
lpFee (pct + total)
timestamp (quote timestamp for LP fee calculation)
isAmountTooLow
quoteBlock
spokePoolAddress
exclusiveRelayer
exclusivityDeadline
expectedFillTimeSec
fillDeadline
limits (see TransferLimits below)

GET /limits

Returns transfer limits for inputToken, outputToken, originChainId, and destinationChainId.

TransferLimits fields

minDeposit
maxDeposit
maxDepositInstant
maxDepositShortDelay
recommendedDepositInstant

GET /available-routes

Returns available bridgeable routes. Filter by any combination of:

originChainId
destinationChainId
originToken
destinationToken

Each route includes token addresses and symbols for both chains.

Manual depositV3 flow

Call /suggested-fees to get fee quote and SpokePool address.
Approve the input token for the origin SpokePool (spokePoolAddress from the response) if needed.
Construct and submit depositV3 on the origin SpokePool with the quote parameters.
Track status via GET /deposit/status.

depositV3 function signature

function depositV3(
    address depositor,           // Address initiating the deposit
    address recipient,           // Address receiving tokens on destination chain
    address inputToken,          // Token address on origin chain
    address outputToken,         // Token address on destination chain
    uint256 inputAmount,         // Amount of inputToken to deposit
    uint256 outputAmount,        // Minimum output amount (inputAmount - totalRelayFee.total)
    uint256 destinationChainId,  // Destination chain ID
    address exclusiveRelayer,    // From /suggested-fees response (address(0) if none)
    uint32 quoteTimestamp,       // timestamp from /suggested-fees response
    uint32 fillDeadline,         // fillDeadline from /suggested-fees response
    uint32 exclusivityDeadline,  // exclusivityDeadline from /suggested-fees response
    bytes message                // Calldata for destination contract (empty bytes if none)
)

Mapping /suggested-fees response to depositV3 parameters

depositV3 param	Source
`inputAmount`	Your original `amount`
`outputAmount`	`amount - totalRelayFee.total`
`exclusiveRelayer`	`exclusiveRelayer` from response
`quoteTimestamp`	`timestamp` from response
`fillDeadline`	`fillDeadline` from response
`exclusivityDeadline`	`exclusivityDeadline` from response
`message`	`0x` (empty) unless using crosschain messages

Call depositV3 on the SpokePool contract at spokePoolAddress from the /suggested-fees response.

Important Notes

Do not cache /suggested-fees responses.
If recipient is an EOA, do not set message.
For embedded crosschain actions with this API, use the legacy guide referenced in the Across docs.