Marex Now Takes USDC as Margin: How Stablecoin Collateral Actually Works, and the Letter It All Rests On

Brokerage and clearing group Marex Group (Nasdaq: MRX) has processed the first live USDC margin posting for CFTC-regulated cleared derivatives. Chicago proprietary trading firm Prime Trading LLC delivered Circle's USDC stablecoin to Marex as initial-margin collateral, with Marex then funding the positions in dollars. The transaction completed the first end-to-end run of a program Marex announced on July 16.

Under the arrangement, Coinbase provides NYDFS-qualified custody, instant 1:1 conversion between USDC and dollars, and reporting infrastructure aligned with CME requirements. Liz Martin, Coinbase's VP of Markets, said in the release that stablecoin collateral is "moving from concept to production." The design keeps the collateral and funding legs separate: USDC is held as an asset an FCM can apply against exposure, while the cash used to support positions remains in dollars.

Regulatory foundation

The workflow rests on CFTC staff no-action relief rather than a formal Commission rule. Staff Letter 25-40, issued on December 8, 2025, permitted FCMs to accept eligible payment stablecoins and certain other non-securities digital assets as customer margin, subject to conditions. The CFTC reissued that letter as 26-05 on February 6, 2026, broadening the definition of payment stablecoin to include coins issued by qualifying national trust banks.

The relief carries conditions on valuation, haircuts, segregation and reporting. During an initial three-month period, participating FCMs may accept only payment stablecoins, bitcoin and ether as digital-asset collateral, and must submit weekly reports on customer digital-asset holdings to the CFTC's Market Participants Division.

CFTC staff clarified in FAQs on March 20, 2026 that the relief is limited to cleared trades. Crypto assets, including payment stablecoins, remain ineligible as initial or variation margin for uncleared swaps under Regulation 23.156. The letters also do not address client deposits of stablecoins into trading accounts, which fall under a broker's own client-money rules; Interactive Brokers has separately begun accepting stablecoin deposits from eligible US clients.

Marex's announcement lands as Coinbase, Visa and Standard Chartered push into stablecoin infrastructure — custody, conversion and reporting — rather than issuance itself. Firms adopting the model still face concentration risk around a small set of custody and conversion providers, and the legal basis remains staff forbearance that can be withdrawn without a formal rule change. Whether other FCMs follow Marex's workflow will be the next indicator of whether USDC margin becomes a standard for cleared derivatives.