US Treasury borrowing costs surge as investors pile into short positions

Something unusual is happening in the repo market, and bond traders are taking notice. Short-term borrowing costs for US Treasuries have jumped sharply, driven by a wave of investors using newly issued two- and five-year notes to build short positions against the market.

The mechanics are straightforward: when a new Treasury note hits the market and becomes the instrument of choice for short sellers, demand to borrow that specific security spikes, pushing repo rates higher. Think of it like every driver in a city suddenly needing to rent the same make and model of car. The rental price goes vertical.

Yields climb, short bets multiply

The two-year Treasury yield climbed 7 basis points on September 18, settling at 4.74%, its highest level since mid-2024. Meanwhile, 10-year yields touched levels not seen since 2007.

The investor positioning data tells an even starker story. A JPMorgan client survey for the week ending September 14 showed short positions in Treasuries surged 10 percentage points in a single week, reaching 19% of surveyed clients. That is the largest one-week increase in short positioning since JPMorgan began tracking the data in 2019.

Net long positioning simultaneously fell to its lowest level since May, and neutral holdings dropped from 56% to 48%.

The Fed is the elephant in the room

The timing is not accidental. Markets were pricing in more than a 90% probability of a 25-basis-point Federal Reserve rate hike at the September 16 meeting, following a fresh round of inflation data and oil price increases tied to geopolitical pressures, including tensions stemming from the Iran conflict.

When investors believe a central bank is going to raise rates, the logical trade is to short shorter-duration Treasuries. Prices fall as yields rise, and the two-year note is especially sensitive to Fed policy expectations.

What this means for markets and investors

For bond investors, the short positioning surge is a warning sign that the path of least resistance for yields remains upward. When 19% of a major bank’s surveyed clients are explicitly betting against Treasuries, and neutral holders are converting to bears rather than bulls, the sentiment backdrop is unambiguously cautious.

The repo market stress itself adds another layer of complexity. Higher borrowing costs for short sellers do not necessarily stop them from shorting. But they do raise the cost of the trade, which means participants need a stronger conviction in the direction of yields to justify the position. The fact that short positioning is still rising despite elevated repo costs suggests that conviction is very much present.

For the broader financial system, rising Treasury yields carry consequences well beyond the bond market. Higher yields on short-term government debt raise the floor for borrowing costs across the economy. Corporate credit, mortgages, auto loans, and even equity valuations are all benchmarked in some way to where risk-free rates sit.