How to settle Circle StableFX trades for USDC and EURC

Circle StableFX is a permissioned institutional request‑for‑quote foreign‑exchange engine on the Arc network that matches off‑chain quotes and settles USDC and EURC on‑chain through an FxEscrow contract. Circle’s documentation, dated Sept. 27, 2026, describes an end‑to‑end flow that ensures both legs of a trade either complete or are cancelled.

A taker begins by requesting a tradable quote through the StableFX API. The taker signs Permit2 EIP‑712 typed data to authorize the escrow to pull funds, creates a trade record, and funds the sell leg into FxEscrow. Makers select confirmed trades, produce EIP‑712 signatures via a presign endpoint, and fund the buy leg. Once both sides have funded, FxEscrow executes payment‑versus‑payment settlement: the taker receives the buy currency less the taker fee, the maker receives the sell currency less the maker fee, and fees are credited to the StableFX fee wallet. Makers may net multiple opposing legs with the same counterparty so only a net amount is required to fund.

Quote tenors are measured from trade creation: instant (30 minutes), hourly (one hour) and daily (one day). After a quote is accepted, both parties have a 10‑minute window to submit required trade signatures before the quote expires. Circle documents a target RFQ response time under 500 milliseconds. The documentation notes common quote failures include unsupported currency pairs and order sizes below minimums; amounts under roughly 10 USDC commonly fail.

Operational prerequisites include an Arc wallet that supports Permit2 and EIP‑712 signing, a Permit2 allowance to the Permit2 contract for the funding token, and API access granted by Circle. Omnibus or pooled wallets are not permitted; each trade must be initiated and completed by the same individually owned wallet. Gas on Arc is payable in Arc USDC.

Circle supplies the APIs and smart contracts but does not custody or move customers’ assets. Firms must fund their own wallets into FxEscrow and remain responsible for licensing and compliance. Circle provides sandbox and production endpoints at api‑sandbox.circle.com for test keys on Arc testnet and api.circle.com for live keys on Arc mainnet, and a browser StableFX Console for non‑code users. Contact for access is available through Circle representatives or sales@circle.com.

The documentation includes endpoint names, status values and example request/response patterns for taker and maker flows. Taker steps include requesting a tradable quote, signing Permit2 typed data, creating a trade and funding as taker. Maker steps include listing confirmed trades, obtaining presignature payloads, submitting EIP‑712 signatures and funding as maker. Funding can be performed via the StableFX API or by calling the FxEscrow contract directly from a web3 stack.

StableFX is described for use by payment service providers, fintech firms, crypto OTC desks, prime brokers and corporate treasuries that hold or can hold USDC/EURC on Arc and that require around‑the‑clock programmable FX settlement outside bank hours. The service is not intended for retail self‑custody swap interfaces, omnibus wallet setups, or firms that require Circle to hold assets end‑to‑end; alternate managed payment products exist for custody use cases.

Developers and operators are advised to map the sandbox quote, Permit2 signing and FxEscrow funding sequence before moving to live traffic and to verify Arc gas expectations. The StableFX documentation is the authoritative technical source for integration details.