Agency MBS Spreads Draw Renewed Interest as Fed Holdings Shrink

The Fed Steps Back, and a Gap Opens

Agency mortgage-backed securities have spent the better part of three years in an awkward position – offering yields that looked attractive on paper but spreads that stubbornly refused to compensate for the uncertainty hanging over the market. That uncertainty had a name: the Federal Reserve, which accumulated more than $2.7 trillion in agency MBS during its quantitative easing programs and then stopped reinvesting principal payments as part of its balance sheet runoff. The resulting overhang weighed on valuations and kept many institutional buyers cautious. Now, with the Fed’s MBS portfolio shrinking at a pace that has meaningfully reduced that overhang, spreads are drawing fresh attention from investors who had largely moved on.

The basic math is starting to work in favor of buyers. As the Fed passively lets its holdings run off through principal and prepayment cash flows, the supply absorption that once fell entirely to private markets is becoming more manageable. Spreads on current-coupon agency MBS relative to comparable Treasuries have widened enough from their post-pandemic tights that yield-focused allocators – particularly insurance companies, pension funds, and bank treasury desks – are revisiting the sector with more genuine interest than they have shown in years.

Why the Fed’s Exit Actually Matters This Time

The Fed’s MBS portfolio peaked somewhere above $2.7 trillion and has been declining steadily since mid-2022 without active sales. Unlike Treasuries, where the Fed could theoretically sell directly into the market, agency MBS runoff depends entirely on mortgage prepayments and scheduled principal payments. That makes the pace inherently slow and tied to housing market activity – which, given elevated mortgage rates, has been subdued. Slower prepayments mean the portfolio shrinks more gradually, but it does shrink, and that directional change matters for market structure.

What this creates is a slow-motion rebalancing of who holds these securities. The Fed’s share of outstanding agency MBS has declined from around a third of the market at peak holdings to a progressively smaller fraction. Private buyers – who demand real spread compensation rather than accepting whatever yield the market offers – are now setting prices in a way they simply could not when the Fed was the dominant marginal buyer. That pricing power has real consequences for where spreads settle.

The practical effect is that agency MBS spreads are moving more in line with traditional supply-demand dynamics. When private investors set the clearing price, sectors that require more active management, like MBS with prepayment optionality baked in, need to offer enough yield premium to justify the complexity. That is exactly the environment where spread widening becomes an opportunity rather than a warning sign, assuming the underlying credit quality – which for agency paper is effectively backed by Fannie Mae, Freddie Mac, or Ginnie Mae – is not in question.

Who Is Actually Buying – and Why

The renewed interest is not coming from a single investor type. Insurance companies with long-duration liabilities have an obvious structural reason to own fixed-income assets with government-adjacent credit profiles. Bank treasuries, navigating capital requirements and liquidity rules, have historically been large holders of agency MBS and are returning to the sector as the yield math improves relative to alternatives like short-term Treasuries or agency debentures. Foreign central banks and sovereign wealth funds, which pulled back during the rate hike cycle, are also showing up again in Treasury data on custody holdings.

Pension funds present a slightly different case. Many are better funded than they have been in decades thanks to the rate rise since 2022, which means liability-driven investing has become more central to their fixed-income allocation decisions. Agency MBS, with its explicit or implicit government guarantee and now-wider spreads, fits neatly into a liability-matching framework – particularly for funds that previously chased corporate credit spreads and now want less default exposure.

The reinvestment of cash flows from maturing fixed-income portfolios is also a factor that does not get enough attention. Institutions that bought agency MBS during the low-rate era and are now receiving principal back from prepayments and maturities need somewhere to put that money. Redeploying into current-coupon agency MBS at today’s spreads means locking in yields that look attractive by any historical comparison over the last decade and a half, without taking on meaningful credit risk. That creates a self-reinforcing demand dynamic as long as spreads stay at current levels or widen further.

There is one complicating factor worth sitting with: prepayment risk is not gone, it is just dormant. With 30-year mortgage rates elevated, homeowners have almost no incentive to refinance. That means the negative convexity embedded in agency MBS – the risk that when rates fall, the bonds get called away at the worst possible moment for investors – is largely theoretical right now. But it will not stay theoretical forever. Any meaningful decline in mortgage rates would accelerate prepayments, shorten durations, and hand investors back their principal at a time when reinvestment rates would presumably be lower. The current spread widening, in part, compensates for that latent risk, but it does not eliminate it.

The Spread Argument Has Limits

Spread investing in agency MBS is not a story about chasing yield into risky territory. The credit case is about as clean as fixed income gets outside of direct Treasury obligations. What makes it complicated is the structure – the embedded optionality, the sensitivity to rate paths, and the way convexity can turn against an investor quickly in a rate-cutting environment. That structural complexity is why spreads need to be meaningfully wider than Treasuries to attract buyers who have other options, and why the current level has started to clear some of the skepticism built up over the last few years.

Defensive fixed-income allocators have increasingly gravitated toward instruments that offer spread pickup without taking on corporate credit risk. Covered bond markets have been seeing similar renewed attention among bank treasurers for comparable reasons – spread over sovereigns with contained credit exposure. Agency MBS occupies a related space in the U.S. fixed-income universe, and the spread widening of the last two years has made the sector competitive again with those alternatives in ways it was not when spreads were compressed to post-crisis tights.

The real question is whether spreads have widened enough to stay wide, or whether a strong wave of institutional buying compresses them again before smaller allocators can act. The Fed is not coming back to buy – its mandate does not currently require it, and there is no political appetite for another round of balance sheet expansion outside of a genuine crisis. That structural absence of the largest buyer in market history is a permanent change in the ecosystem, not a temporary one. Whether that absence is ultimately bullish for spreads depends entirely on how aggressively private capital decides to fill the gap, and at what price it insists on doing so.