A. Security Valuation: Securities are valued as of the close of trading on the New York Stock Exchange (generally 4 p.m., Eastern time) on the valuation date. Bonds and other temporary cash investments are valued using the latest bid prices or using valuations based on a matrix system (which considers such factors as security prices, yields, maturities, and ratings), both as furnished by independent pricing services. Structured debt securities, including mortgages and asset-backed securities, are valued using the latest bid prices or using valuations based on a matrix system that considers such factors as issuer, tranche, nominal or option-adjusted spreads, weighted average coupon, weighted average maturity, credit enhancements, and collateral, as furnished by independent pricing services. Investments in Vanguard Market Liquidity Fund are valued at that fund's net asset value.
Securities for which market quotations are not readily available, or whose values have been affected by events occurring before the fund's pricing time but after the close of the securities’ primary markets, are valued by methods deemed by the valuation designee to represent fair value and subject to oversight by the board of trustees.
B. Foreign Currency: Securities and other assets and liabilities denominated in foreign currencies are translated into U.S. dollars using exchange rates obtained from an independent third party as of the fund’s pricing time on the valuation date. Realized gains (losses) and unrealized appreciation (depreciation) on investment securities include the effects of changes in exchange rates since the securities were purchased, combined with the effects of changes in security prices. Fluctuations in the value of other assets and liabilities resulting from changes in exchange rates are recorded as unrealized foreign currency gains (losses) until the assets or liabilities are settled in cash, at which time they are recorded as realized foreign currency gains (losses).
C. To Be Announced (TBA) Transactions: A TBA transaction is an agreement to buy or sell mortgage-backed securities with agreed-upon characteristics (face amount, coupon, maturity) for settlement at a future date. The fund may be a seller of TBA transactions to reduce its exposure to the mortgage-backed securities market or in order to sell mortgage-backed securities it owns under delayed-delivery arrangements. When the fund is a buyer of TBA transactions, it maintains cash, short-term investments, or Treasuries in an amount sufficient to meet the purchase price at the settlement date of the TBA transaction. The primary risk associated with TBA transactions is that a counterparty may default on its obligations. The fund mitigates its counterparty risk by, among other things, performing a credit analysis of counterparties, allocating transactions among numerous counterparties, and monitoring its exposure to each counterparty. The fund may also enter into a Master Securities Forward Transaction Agreement (MSFTA) with certain counterparties and require them to transfer collateral as security for their performance. In the absence of a default, the collateral pledged or received by the fund cannot be repledged, resold, or rehypothecated. Under an MSFTA, upon a counterparty default (including bankruptcy), the fund may terminate any TBA transactions with that counterparty, determine the net amount owed by either party in accordance with its MSFTA, and sell or retain any collateral held up to the net amount owed to the fund under the MSFTA.
At December 31, 2024, counterparties had deposited in segregated accounts cash of $10,000 in connection with TBA transactions.
D. Mortgage Dollar Rolls: The fund enters into mortgage-dollar-roll transactions, in which the fund sells mortgage-backed securities to a dealer and simultaneously agrees to purchase substantially similar securities in the future at a predetermined price on a predetermined date. The fund forgoes principal and interest paid on the securities sold. In exchange for the forgone principal and interest paid, the fund is compensated by investing the proceeds of the sale, typically in high-quality short-term fixed income securities, and earning interest on such investments. Further the fund receives a lower price on the securities to be repurchased. The fund also enters into mortgage-dollar-roll transactions in which the fund buys mortgage-backed securities from a dealer pursuant to a TBA transaction and simultaneously agrees to sell substantially similar securities in the future at a predetermined price. The securities bought in mortgage-dollar-roll transactions are used to cover an open TBA sell position. The fund continues to earn interest on mortgage-backed security pools already held and receives a lower price on the securities to be sold in the future. The fund accounts for mortgage-dollar-roll transactions as purchases and sales; as such, these transactions may increase the fund’s portfolio turnover rate. Amounts to be received or paid in connection with open mortgage dollar rolls are included in Receivables for Investment Securities Sold or Payables for Investment Securities Purchased.
E. Options: The fund invests in options contracts on futures to adjust its exposure to the underlying investments. The primary risk associated with purchasing options is that if interest rates move in such a way that the exercise price of the option exceeds the value of the underlying investment, the position is worthless at expiration, and the fund loses the premium paid. The primary risk associated with selling options is that if interest rates move in such a way that the exercise price of the option exceeds the value of the underlying investment, the counterparty exercises the option, and the fund loses an amount equal to the market value of the option written less the premium received. Counterparty risk involving options on futures contracts is mitigated because a regulated clearinghouse is the counterparty instead of the clearing broker. To further mitigate counterparty risk, the fund trades options on futures contracts on an exchange, monitors the financial strength of its clearing brokers and clearinghouses, and has entered into clearing agreements with its clearing brokers.
Options contracts on futures are valued at their quoted daily settlement prices. The premium paid for a purchased option is recorded as an asset that is subsequently adjusted daily to the current market value of the option purchased. The premium received for a written option is recorded as an asset with an equal liability that is subsequently adjusted daily to the current market value of the option written. Fluctuations in the value of the options are recorded as unrealized appreciation (depreciation) until expired, closed, or exercised, at which time realized gains (losses) are recognized.
F. Swaptions: The fund invests in options on swaps, which are transacted over-the-counter (OTC) and not on an exchange. The fund enters into swaptions to adjust the fund's sensitivity to interest rates or to adjust its exposure to the underlying investments. The fund may purchase a swaption from a counterparty whereby the fund has the right to enter into a swap in which the fund will pay either a fixed percentage rate or a floating rate, which is reset periodically based on short-term interest rates, and receive a different floating rate, each applied to a notional amount. The fund may also sell a swaption to a counterparty whereby the fund grants the counterparty the right to enter into a swap in which the fund will pay a floating rate and receive a fixed rate, each applied to a notional amount. Swaptions also include options that allow an existing swap to be terminated or extended by one of the counterparties. Unlike exchange-traded options, which are standardized with respect to the underlying instrument, expiration date, contract size, and strike price, the terms of OTC options generally are established through negotiation with the other party to the option contract. Although this type of
