Over the past three weeks investors pulled cash from US mortgage bond funds at an unusually rapid pace, with outflows ranking among the seven largest since early 2021; the US mortgage‑backed securities (MBS) index posted its second‑worst monthly return on record in September. Treasury yields climbed to multi‑decade highs after oil jumped, inflation worries rose and markets priced in more Fed tightening, triggering MBS selling. MBS are highly sensitive to sudden moves in Treasury yields because h

Over the past three weeks investors pulled cash from US mortgage bond funds at an unusually rapid pace, with outflows ranking among the seven largest since early 2021; the US mortgage‑backed securities (MBS) index posted its second‑worst monthly return on record in September. Treasury yields climbed to multi‑decade highs after oil jumped, inflation worries rose and markets priced in more Fed tightening, triggering MBS selling. MBS are highly sensitive to sudden moves in Treasury yields because higher rates curb refinancing, extending the time investors hold lower‑coupon securities and raising duration risk. Fed tightening and a flatter yield curve could further weaken banks — a key MBS buyer — reducing demand. Strategist Erica Adelberg says the offset is that mortgage rates, now the highest since 2023, should suppress refinancing and homebuying, likely slowing house‑price and loan growth and trimming MBS supply toward year‑end.