A mysterious capital influx targeted a highly rate-sensitive exchange-traded fund precisely one day before the U.S. Treasury announced an expansion of its long-dated bond repurchase program, reigniting speculation about potential information leaks and insider trading activity.

The Treasury revealed on Wednesday, August 20th, plans to at least double the size of its buyback operations for 10- to 30-year notes. In response, the 30-year Treasury yield dropped as much as 10 basis points during the session to 5.18%, retreating from near two-decade highs.

Just one day prior to that announcement, on Tuesday, the Pimco 25+ Year Zero Coupon U.S. Treasury Index ETF recorded $123 million in daily net inflows, marking its strongest single-day intake on record. Trading volume also surged to 5.2 million shares, nearly double the previous peak seen in 2024.

Following the news on Wednesday, the ETF jumped 3.2% in a single session, its largest one-day gain since November 2024.

Why Is This ETF So Sensitive?

This fund, which manages approximately $1.5 billion in assets, focuses on STRIPS—zero-coupon instruments created by separating the principal and interest components of Treasury bonds.

Since zero-coupon bonds make no periodic interest payments and deliver all returns at maturity, their prices react far more aggressively to interest rate shifts than traditional bonds. The ETF carries an effective duration of roughly 28 years, implying that for every 1 percentage point decline in long-term yields, its net asset value could theoretically climb by about 28%.

If a standard long-duration bond ETF resembles a conventional sedan, this particular fund is more like a high-performance race car—navigating the same turns with far greater amplitude in response.

For this reason, the ETF stands as one of the most direct and leveraged instruments available for betting on long-end yield movements.

Perfect Timing Raises Questions

The Treasury's buyback announcement came as a genuine surprise, with no prior market expectation of such a move.

Yet on the day before the disclosure, an investor aggressively accumulated positions in this highly sensitive ETF, with both inflow and volume figures reaching unprecedented levels. This timing has fueled speculation over whether certain parties had advance knowledge of the policy decision.

This is not the first such controversy in U.S. markets. Around the previous administration's tariff pause announcements, abnormal options trading activity similarly sparked widespread debate over potential White House-related insider information.

As of now, no specific source for these capital flows has been identified, and no regulatory body has publicly confirmed an active investigation into the matter.

Long Bonds Still Under Pressure This Year

Despite the sharp single-day rally, the ETF remains down 5.4% year-to-date.

Persistently elevated inflation expectations combined with concerns over fiscal deficits have kept sustained selling pressure on long-dated Treasuries, with the 30-year yield briefly approaching levels not seen in nearly two decades.

While the expanded Treasury buyback program provides short-term support for long-dated bonds, opinions remain divided on whether it can reverse the broader downward trend for the year.