The mechanism. The GENIUS Act, signed into law in July 2025, doesn't just legalize stablecoins — it dictates exactly where the money backing them has to sit. Issuers must hold reserves 1:1 in cash, insured-bank demand deposits, Treasury bills of 93 days or less, and short-dated repo collateralized by those bills. Reserves can't be rehypothecated except narrowly for redemption liquidity, and custody must sit with a bank, credit union, SEC-registered entity, or CFTC-regulated custodian that segregates the assets from its own balance sheet. That's a federal mandate to route a fast-growing pool of dollars — Circle alone runs tens of billions in reserves — through a small set of qualified custodians and government money-market funds. Every dollar of stablecoin issuance now has to pass through someone's custody ledger and someone's Treasury money-market fund before it can back a token. That's fee income on float that scales with stablecoin supply, not with issuer profit margins.
Who cashes in. The clearest beneficiary is the custody-and-asset-management layer sitting underneath the issuers, not the issuers themselves. Coinbase (COIN) co-founded Circle's USDC arrangement and earns a contractual share of reserve interest income from Circle's reserve portfolio — a claim on the Treasury yield generated by USDC float that doesn't depend on Coinbase's trading volumes at all, and grows automatically as USDC's regulatory tailwind expands issuance. Robinhood (HOOD) is pushing further into stablecoin infrastructure and tokenized products, positioning to capture the same custody/cash-management fee stack as compliant stablecoin rails scale under a codified federal regime. Traditional custody banks that already service Circle-style reserve structures — the BNY Mellon/BlackRock model, where a 2a-7 government money-market fund holds the Treasuries and a global custodian holds the fund — are the purest expression of this thesis: they earn custody and fund-management fees on reserve balances regardless of which stablecoin brand wins market share.