The State Street SPDR Portfolio Mortgage Backed Bond ETF (SPMB) aims to mirror the price and yield performance of the Bloomberg U.S. MBS Index, prior to accounting for fees and expenses. This cost-effective exchange-traded fund provides exposure to investment-grade agency mortgage-backed securities within the U.S. bond market. It is part of the State Street SPDR Portfolio lineup, a series of low-cost funds designed as core components for broad diversification across key asset classes. The fund's portfolio undergoes rebalancing on the last business day of each month.