MBS OAS Widens to 112bps as 5.19% Treasury Yield Paralyzes Prepayment Models
2026-11-10, FP360 — Option-adjusted spreads on 30-year agency MBS have widened to 112 basis points over the 5.19% Treasury yield, as the lock-in effect from 6.72% mortgage rates suppresses prepayment speeds to record lows and forces duration hedging to run hot.
MBS duration is extending faster than models predict; investors should underweight convexity and favor specified pools with low loan balances.
Specified pools with low loan balances (<=$150k) and high FICO scores offer prepayment protection and yield 85bps over Treasuries.
A sudden drop in mortgage rates below 6% could trigger a prepayment wave, extending duration losses for passive MBS holders.
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- What Happened: The option-adjusted spread (OAS) on 30-year agency MBS widened to 112bps over the 5.19% 10-year Treasury yield, the highest since March 2025, as prepayment speeds collapsed to 4.2 CPR.
- Hidden Mechanism: With 6.72% mortgage rates, 99% of outstanding loans are out-of-the-money to refinance, creating a “lock-in” effect that extends duration and forces servicers to hedge with Treasuries, amplifying yield volatility.
- Capital Transmission: Liquidity is rotating from current-coupon MBS into short-duration T-bills (4.25% yield) and specified pools, while dealers warehouse risk at 2011-level spreads.
The Prepayment Squeeze: Why Duration Is Extending
Mortgage-backed securities are trapped in a prepayment desert. With the 30-year fixed mortgage rate at 6.72% and the 10-year Treasury at 5.19%, the average outstanding mortgage coupon of 3.8% is deeply out-of-the-money. As a result, prepayment speeds (CPR) have collapsed to 4.2%—a level last seen during the 2020 refi boom, but for the opposite reason. This means MBS investors who expected their principal back are now holding longer-duration paper, extending the average life of a 30-year MBS from 7.2 years to 9.8 years. The market is forcing a repricing of convexity risk, and the 112bps OAS reflects that uncertainty.
The Fed’s Balance Sheet Runoff: A Slow Bleed for MBS
While the Fed has slowed its Treasury runoff, it continues to let mortgage-backed securities roll off its balance sheet at a pace of $35 billion per month. This adds to the supply that dealers must absorb, but with the fed funds rate at 4.25% (the top of the range), banks are reluctant to warehouse duration. The result is a buyer’s strike: money managers are demanding a premium to hold MBS, and the OAS is widening. The Fed’s own MBS holdings now stand at $2.1 trillion, down from $2.7 trillion at the peak, but the market is not yet clear on when the runoff will end.
Why the Fed Funds Rate Is a Range (and Why It Matters for MBS)
The Fed funds rate is a range (currently 4.00-4.25%) because the Fed targets a band, not a single rate, to accommodate daily fluctuations in bank reserves. For MBS investors, this means the short-term funding cost for leverage is anchored at the top of the range (4.25%), which sets a floor for carry. With the 10-year at 5.19%, the curve is positively sloped, but the volatility in the long end makes hedging expensive. The range also signals the Fed’s caution: it is not eager to cut rates aggressively, which keeps prepayment risk low in the near term but leaves the door open for a sudden shift if the economy weakens.
Positioning & Liquidity Map: Who Is Trapped?
The trapped players are bank portfolios and REITs that loaded up on MBS in 2023-2024 at wider spreads, only to see duration extend. These investors are now forced to hedge with Treasury futures, paying up for protection. The marginal buyer is money managers and ETFs that are attracted by the 112bps spread, but they are demanding specified pools with lower loan balances to mitigate prepayment risk. Dealer inventories are near $120 billion, up from $80 billion a year ago, and their hedging activity is adding to Treasury market volatility. A further widening in OAS could force margin calls for leveraged players, creating a feedback loop.
Forward Scenarios & Probability Matrix
| Scenario | Implied Probability | Key Trigger / Level | Expected Asset Reaction |
|---|---|---|---|
| Base Case | 55% | 10Y yield stays in 5.00-5.40% range; prepayments remain below 5 CPR | MBS OAS tightens to 100-105bps as carry attracts buyers |
| Bullish Tail | 25% | 10Y yield breaks below 4.80%, mortgage rates fall to 6.2% | OAS widens to 130bps; duration extends further, prices fall |
| Bearish Stress | 20% | 10Y yield spikes above 5.50%, triggering margin calls | Forced selling in MBS, OAS blows out to 150bps, spillover to Treasuries |
Dorian Reed
Computational Econometrician. Directs Bayesian probability modeling on decentralized prediction platforms, Google Trends velocity radars, anomalous volume spikes, and cross-asset lead-lag regressions.