To pursue its goal, the fund generally invests in securities that are included in the Bloomberg US Long Treasury Index. The index includes all publicly issued, U.S. Treasury securities that have a remaining maturity of ten or more years, are rated investment grade, and have dollar 300 million or more of outstanding face value. The securities in the index must be denominated in U.S. dollars and must be fixed rate and non-convertible. The index excludes U.S. Treasury stripped securities. The index is market capitalization weighted and the securities in the index are updated on the last business day of each month. As of December 31, 2023, there were 80 securities in the index.