Feb 25, 2026 / Academic Paper

Unmasking the CUSIP-Level Concentration Risk in Stablecoins

Stablecoin reserves are clustering into a tiny subset of US Treasuries. This Sesame Vault report analyzes how the GENIUS Act creates systemic risk through CUSIP concentration.

Executive Overview

The emergent concentration of stablecoin reserve portfolios into a narrow set of Treasury bill CUSIPs represents a critical structural risk overlooked in initial regulatory discussions. This Sesame Vault analysis examines how $310 billion in current reserves—projected to reach trillions—could destabilize the Treasury and repo markets due to the restrictive 93-day maturity mandate of the GENIUS Act.

Key Findings

  • The GENIUS Act restricts reserves to Treasury bills with maturities of less than 93 days, funneling the entire sector into a pool of approximately 25 distinct CUSIPs.
  • While the total Treasury market is $30.3 trillion, the sub-93-day eligible universe is only ~$4.5 trillion; stablecoins already claim 12% of this pool.
  • At a projected $2 trillion scale, stablecoin reserves would absorb 80% of the eligible universe, a level that would likely distort monetary policy and yield curves.
  • Transparency is a major gap: while Circle and Ripple provide CUSIP-level disclosure, Tether accounts for a significant share of the sector’s Treasury bill holdings but does not provide CUSIP-level allocation breakdowns in publicly available reporting.
  • Systemic transmission of stress would likely move from redemptions to dealer exhaustion, then into the $12.6 trillion repo market and leveraged basis trades.
  • Stablecoin issuance creates "net-new" Treasury demand from sources such as offshore dollar demand and emerging markets, rather than just reshuffling existing money market assets.

Why CUSIP Concentration Matters for U.S. Financial Stability

The concentration problem is not merely a matter of asset quality; it is a matter of intermediation capacity. By forcing all compliant stablecoin issuers to hold the same short-dated instruments, the GENIUS Act makes correlated liquidation events structurally inevitable. If multiple issuers attempt to sell the same CUSIPs simultaneously, the volume would likely exceed the warehouse capacity of primary dealers.

This creates a "liquidity misconception": an asset that is individually safe because of its short maturity becomes systemically illiquid when the entire market is "crowded" into the same 25 identifiers. For the Treasury, this dependency creates fiscal risk; a sharp contraction in the stablecoin market would leave a massive hole in T-bill auction demand, potentially forcing the Treasury to shift its borrowing strategy under duress.

The institutions and regulators that address this gap by broadening eligible maturities or mandating CUSIP-level transparency will be essential in converting stablecoin demand into a stable long-term support for U.S. dollar dominance.

What's Inside the Report

The full analysis provides a quantitative evidence base spanning CUSIP-level portfolio data, BIS empirical research on yield impacts, and a five-stage systemic transmission model. It includes detailed arithmetic on CUSIP-level outstanding volume, a comparison of GENIUS Act requirements versus SEC Rule 2a-7 for money market funds, and five specific policy recommendations for the Department of the Treasury.

Frequently Asked Questions

What is CUSIP-level concentration risk?

It is the risk that arises when multiple large financial actors hold identical, specific Treasury securities (identified by CUSIP numbers). If they all need to sell at once, the market for those specific securities can freeze, even if the broader Treasury market remains functional.

How does the GENIUS Act contribute to this risk?

Section 4(a)(1)(A) of the Act restricts "eligible reserve assets" to Treasury bills and notes with remaining maturities of 93 days or less. This forces the entire stablecoin industry into a very small subset of the total Treasury market.

Why isn't a 93-day maturity enough to ensure liquidity?

While short maturity ensures the asset will return to part value at maturity, it does not guarantee it can be sold today without impacting the price. True liquidity requires market depth, which is compromised when all participants are forced into the same few securities.

What are the "Five Stages" of systemic transmission?

The report identifies a chain reaction starting with a redemption trigger, followed by concentrated liquidation of identical CUSIPs, dealer balance sheet exhaustion, repo market volatility, and finally contagion into leveraged basis trades across the yield curve.

Download the Paper

For a detailed briefing on stablecoin reserve concentration, CUSIP-level modeling, or the structural implications for Treasury debt management, contact Sesame Vault Inc. here. We are available for departmental advisement and technical briefings.