GasConfig controls who covers the Stellar transaction fee. The type is a discriminated union
with exactly two members - any other value fails to type-check:
Sponsored mode
The facilitator’s sponsor account pays the XLM fee on behalf of the payer. The payer signs only theSorobanAuthorizationEntry off-chain; the facilitator wraps it in a fee-bump
transaction, supplies the XLM, and submits to the network.
The payer needs zero XLM - not to transact, and not even to exist on-chain. This is the
default for most applications. See Onboarding to understand how an
account with no XLM balance is materialized in the first place.
Token-fee mode
{ mode: "token", token } lets the payer cover the fee in USDC instead of XLM. The
facilitator still fronts the XLM gas; the FeeForwarder contract collects reimbursement
from the payer’s stablecoin balance in a single authorization entry - the payer signs once.
Use token-fee when you want the user, not your sponsor, to bear the gas cost in the
asset they already hold.
See Gas in token for the full details: the FeeQuote fields,
the maxFee ceiling, and the TOKEN_GAS_REJECTED error code.
Choosing a mode
The
GasConfig type only admits these two members. Passing an undeclared mode is a
compile-time error - you cannot accidentally configure something unsupported.Next
Gas in token
Full reference for the USDC fee-forwarding mode: FeeQuote, maxFee, and error codes.
Onboarding
How a payer with zero XLM gets a payment-ready account, sponsored end-to-end.