Strategy. In seeking to track the performance of the Bloomberg U.S. MBS Index ? (the Index), the Fund employs a sampling strategy, which means that the Fund is not required to purchase all of the securities represented in the Index. Instead, the Fund may purchase a subset of the securities in the Index in an effort to hold a portfolio of securities with generally the same risk and return characteristics of the Index. The quantity of holdings in the Fund will be based on a number of factors, including asset size of the Fund. Based on its analysis of these factors, SSGA Funds Management, Inc. (SSGA FM or the Adviser), the investment adviser to the Fund, either may invest the Fund's … Show more… In seeking to track the performance of the Bloomberg U.S. MBS Index ? (the Index), the Fund employs a sampling strategy, which means that the Fund is not required to purchase all of the securities represented in the Index. Instead, the Fund may purchase a subset of the securities in the Index in an effort to hold a portfolio of securities with generally the same risk and return characteristics of the Index. The quantity of holdings in the Fund will be based on a number of factors, including asset size of the Fund. Based on its analysis of these factors, SSGA Funds Management, Inc. (SSGA FM or the Adviser), the investment adviser to the Fund, either may invest the Fund's assets in a subset of securities in the Index or may invest the Fund's assets in substantially all of the securities represented in the Index in approximately the same proportions as the Index, as determined by the Adviser to be in the best interest of the Fund in pursuing its objective. Under normal market conditions, the Fund generally invests substantially all, but at least 80%, of its total assets in the securities comprising the Index and in securities that the Adviser determines have economic characteristics that are substantially identical to the economic characteristics of the securities that comprise the Index. TBA Transactions (as defined below) are included within the above-noted investment policy. In addition, in seeking to track the Index, the Fund may invest in debt securities that are not included in the Index. The Fund may also invest in cash and cash equivalents or money market instruments (including money market funds advised by the Adviser) for cash management purposes. In seeking to track the Index, the Fund's assets may be concentrated in an industry or group of industries, but only to the extent that the Index concentrates in a particular industry or group of industries. The Index is designed to measure the performance of the U.S. agency mortgage pass-through segment of the U.S. investment grade bond market. The term U.S. agency mortgage pass-through security refers to a category of pass-through securities backed by pools of mortgages and issued by one of the following U.S. government-sponsored enterprises: Government National Mortgage Association (GNMA); Federal National Mortgage Association (FNMA) and Federal Home Loan Mortgage Corporation (FHLMC). The Index is formed by grouping the universe of individual fixed rate mortgage backed securities pools into generic aggregates according to the following parameters: (i) agency; (ii) program; (iii) pass-through coupon; and (iv) origination year. Index maturity and liquidity criteria are then applied to these aggregates to determine which qualify for inclusion in the Index. To be included in the Index, securities must be fixed rate, denominated in U.S. dollars, and be part of a cohort that has $1 billion or more of outstanding face value and have a weighted average maturity of at least one year. Excluded from the Index are buydowns, graduated equity mortgages, project loans, manufactured homes (dropped in January 1992), graduated payment mortgages (dropped in January 1995), non-agency (whole loan) securities, jumbo securities, collateralized mortgage obligations, and hybrid adjustable-rate mortgages. The Index is market capitalization weighted and the securities in the Index are updated on the last calendar day of each month. As of July 31, 2025, there were 1,048 securities in the Index. Transactions in mortgage pass-through securities may occur through standardized contracts for future delivery in which the exact mortgage pools to be delivered are not specified until a few days prior to settlement, referred to as a to-be announced transaction or TBA Transaction. In a TBA Transaction, the buyer and seller agree upon general trade parameters such as agency, settlement date, par amount and price. The actual pools delivered generally are determined two days prior to the settlement date. The Fund expects to enter into such contracts on a regular basis, and pending settlement of such contracts, the Fund will invest its assets in liquid, short-term instruments, including shares of money market funds advised by the Adviser or its affiliates. The Index is sponsored by Bloomberg Index Services Limited (the Index Provider), which is not affiliated with the Fund or the Adviser. The Index Provider determines the composition of the Index, relative weightings of the securities in the Index and publishes information regarding the market value of the Index. Show less