The Circle Forwarding Service is a service for CCTP that simplifies integration
by removing the need for you to run multichain infrastructure. This can improve
user experience for crosschain transfers by ensuring reliability and eliminating
the need to handle destination chain gas fees.
How it works
A CCTP transfer without the Forwarding Service is a three-step process:
- Create a transaction to burn USDC on the source chain and wait for Circle to
sign an attestation.
- Request an attestation from the Circle API.
- Create a transaction to mint USDC on the destination chain.
This process requires you to have a wallet that can sign transactions on the
source and destination chains, and native tokens for paying the transaction gas
fee on both chains.
You use the Forwarding Service by including a forward request in the hook data
of the burn transaction on the source chain. Circle validates the hook data,
signs the attestation, and broadcasts the mint transaction on the destination
chain for you, removing the need for you to handle the transaction on the
destination chain.
For a full example of how to use the Forwarding Service, see
Transfer USDC with the Forwarding Service.
The hook data for Forwarding Service begins with the reserved magic bytes
cctp-forward followed by versioning and payload fields. You can append your
own custom hook data after Circle’s reserved space. Forwarding Service doesn’t
support forwarding to wrapper contracts (for example, when destinationCaller
is set).
| Bytes | Type | Data |
|---|
| 0-23 | bytes24 | cctp-forward |
| 24-27 | uint32 | Version, set to 0 |
| 28-31 | uint32 | Length of additional Circle hook data, set to 0 |
| 32-51 | any | Developer-defined hook data |
// Includes magic bytes ("cctp-forward") + hook version (0) + empty data length (0)
const forwardHookData =
"0x636374702d666f72776172640000000000000000000000000000000000000000";
Fees and execution
The Forwarding Service charges a fee for each transfer, in addition to the CCTP
protocol fee. The Forwarding Service fee charged is to cover gas costs on the
destination chain and a small service fee. The Forwarding Service prioritizes
fast execution and quotes gas dynamically. If gas used is less than gas needed
for execution, the remainder is spent as an additional priority fee where they
are supported. On all chains, a higher fee provides a safety buffer for
successful transaction delivery on the destination chain. Circle does not refund
for excess gas and does not keep the excess gas, except in cases where excess
priority fess are rejected.
The
depositForBurnWithHook
transaction includes a maxFee parameter. When using the Forwarding Service,
this parameter should be set to a value that is large enough to cover the CCTP
protocol fee and the Forwarding Service fee. Because the gas budget for the
destination chain comes from a USDC fee on the source chain, choosing a lower
maxFee results in a lower priority fee on the destination chain. A higher
maxFee results in a higher priority fee on the destination chain and can
result in faster confirmation.
The Forwarding Service charges a service fee for each transfer:
| Destination chain | Service fee (USDC) |
|---|
| Ethereum | $1.25 |
| All other chains | $0.20 |
If the maxFee parameter is insufficient to cover the both Fast Transfer
protocol fee and the Forwarding Service fee, CCTP will prioritize forwarding
execution over Fast Transfer. This means that the transfer will execute as a
Standard Transfer with the Forwarding Service.
Supported blockchains
For a full list of supported blockchains, see
CCTP Supported Blockchains. 
