The $1.5 billion PIMCO 25+ Year Zero Coupon U.S. Treasury Index ETF (ZROZ) received a record $123 million inflow on Tuesday, one day before the Treasury announced an expansion of its buyback scale. Trading volume reached 5.2 million shares, nearly twice the previous high set in 2024. ZROZ primarily holds STRIPS (separately traded Treasury principal and interest securities), giving it an effective duration of about 28 years. In theory, a 1-percentage-point decline in yields would lift its bond prices by roughly 28%, making the fund a highly sensitive instrument for expressing views on long-term U.S. interest rates. The ETF rose 3.2% on Wednesday, its largest single-day gain since November 2024.