Agency MBS Spreads Are Moving, and Fixed Income Allocators Are Paying Close Attention
Agency mortgage-backed securities have spent the better part of two years in a kind of purgatory – wide enough to attract interest, but burdened by the Federal Reserve’s massive holdings and the uncertainty around when and how fast those holdings would shrink. Now, with quantitative tightening slowing to a near-crawl, the calculus around agency MBS spreads is shifting in ways that fixed income desks haven’t seen in some time.
The Fed’s balance sheet reduction program, which at its peak was pulling roughly $35 billion per month in agency MBS off the books through passive runoff, has effectively decelerated. Mortgage prepayment speeds have slowed dramatically in a higher-rate environment, meaning fewer loans are paying off early and the Fed’s portfolio is declining at a trickle rather than a flood. That dynamic has a direct bearing on spread levels – and on how investors should be positioning in the agency MBS market right now.
Why the Fed’s Pace Matters So Much for MBS Spreads
Agency MBS spreads – typically measured against comparable Treasury yields or swap rates – are highly sensitive to supply and demand dynamics. When the Fed was an active buyer, it absorbed enormous quantities of agency MBS from the market, compressing spreads to historically tight levels. When it shifted to runoff mode, the implicit backstop disappeared, and spreads widened to reflect the reality of a market that had to price in additional supply risk without the central bank as a guaranteed buyer.
Now that runoff has slowed, the supply pressure has eased somewhat. The Fed is no longer a seller – it never was – but the absence of reinvestment has the same functional effect over time. With prepayments crawling in a rate environment where few homeowners have any incentive to refinance, the Fed’s MBS portfolio is essentially frozen in place. That means less passive supply hitting the market than many allocators originally modeled, and spread levels have begun to reflect it.
Reading the Spread Levels
Agency MBS spreads, particularly on 30-year current coupon securities, have hovered in ranges that represent genuinely attractive compensation relative to Treasuries when viewed against historical norms. The current coupon spread – a benchmark measure of where newly originated mortgage pools price – has remained elevated compared to the pre-2022 era, even as rate volatility has introduced significant uncertainty into duration management.
The core reason spreads remain wide despite the Fed slowdown is rate volatility itself. Agency MBS carry negative convexity: as rates fall, prepayments accelerate and investors get their money back faster than they’d prefer; as rates rise, prepayments slow and investors are stuck holding longer-duration assets at below-market yields. The embedded option that homeowners hold – to refinance or pay off early – has real cost, and that cost is reflected in the spread premium investors demand.
What makes the current environment somewhat unusual is that both factors – the supply-side pressure from Fed runoff and the demand-side drag from rate volatility – are moderating at the same time. The Fed isn’t flooding the market with new supply, rate volatility has come off its 2022-2023 peaks, and the underlying credit quality of agency MBS (backed by Fannie Mae, Freddie Mac, or Ginnie Mae) is not in question. That combination has some fixed income allocators revisiting positions they had trimmed or avoided.
For allocators already watching rate-sensitive instruments closely – including those who have been building positions in putable bonds as a hedge against rate uncertainty – agency MBS at current spread levels offer a different kind of optionality: a government-backed yield pickup that doesn’t require taking on credit risk.
Who Is Actually Buying
Banks, historically the largest non-Fed holders of agency MBS, have been cautious given their own liability management challenges. Rising deposit costs have pressured net interest margins, and holding long-duration assets carries mark-to-market risk that many regional banks are now acutely aware of after the events of 2023. Demand from the domestic banking sector has been softer than in prior cycles.
The buyers stepping in are largely institutional – insurance companies seeking yield to match long-term liabilities, pension funds rebalancing into fixed income as equities have delivered strong returns, and international investors attracted by both the yield differential and the implicit government backing. Money managers running core and core-plus bond strategies have also been adding agency MBS exposure as a way to pick up spread without venturing into corporate credit or structured products with less certain cashflows.
The Forward Question: What Happens When the Fed Eventually Pivots?
The scenario that agency MBS bulls are quietly counting on is a Fed that, at some point, either stops runoff entirely or begins reinvesting. Either action would remove supply from the market in a real and sustained way. If the Fed eventually shifts to active reinvestment – which it has done before – agency MBS would benefit from a buyer with a balance sheet that dwarfs any private sector participant. That optionality is part of what makes current spread levels interesting to long-horizon allocators.
Against that, the bear case is straightforward: if rates fall meaningfully, prepayments will accelerate, and the negative convexity problem returns in full force. Investors who bought at current spread levels expecting to hold through a rate-cutting cycle could find their bonds shortening faster than expected, forcing reinvestment at lower yields. The spread pickup works best in a range-bound rate environment – exactly the kind that is easier to assume than to actually get.
The more technical risk is that spread widening can happen independently of rate moves. If bank demand stays muted, if foreign buyers rotate elsewhere, or if the Fed’s own communications around balance sheet policy shift unexpectedly, spreads could cheapen even without a dramatic move in underlying Treasury yields. Agency MBS is a market where technical flows – not just fundamentals – have driven outsized price moves in recent years, and that pattern is unlikely to change simply because the immediate supply pressure has eased. That reality is what keeps even the most constructive allocators from going all-in: the spread looks right, but the market has a habit of making spreads look wrong before they eventually correct.
