Jumbo rates behave differently from conforming rates because banks fund them, so pricing follows each bank's cost of funds rather than the Fannie/Freddie machinery. Most jumbo loans either sit on a bank's own books in portfolio or get securitized in much smaller pools, sometimes sold to a large bank. The mechanism: - Cheap money, hungry banks. When a bank's cost of funds is low, large high-quality loans (bigger down payments, stronger credit, better performance) are attractive, because the spread between what the bank pays for money and the mortgage rate is wide. - Expensive money, no appetite. When the cost of funds rises, that spread compresses and jumbo lending dries up, so pricing gets far less competitive. - No runoff, no need. In a slow environment, few borrowers refinance or sell, so few loans roll off the books. Without runoff, a bank has little need to replace loans, and the thin margin on new jumbos is often not worth chasing even for existing customers. When jumbo pricing looks out of whack next to conforming, it usually traces back to bank funding costs and appetite rather than the broader bond market. The fix is to shop lenders who are actively pricing jumbo, because appetite varies a lot from one institution to the next.