Class I Shares
 Summary ProspectusMay 1, 2017
  
     Your costs would be higher if fees or sales charges imposed by a Variable Contract for which the portfolio is an investment option were included.
 Annual portfolio operating expenses(expenses that you pay each year as a percentage of the value of your investment)Class IManagement Fees0.40%Distribution and Service (12b-1) Fees0.00%Other Expenses0.29%Acquired Fund Fees and Expenses10.01%Total Annual Portfolio Operating Expenses Plus Acquired Fund Fees and Expenses0.70%Fee Waiver and Expense Limitation2–0.07%Total Annual Portfolio Operating Expenses Plus Acquired Fund Fees and Expenses After Fee Waiver and Expense Limitation20.63%
 1Total annual portfolio operating expenses in the table, before and after fee waiver and expense reimbursements, may be higher than the corresponding ratio of expenses to average net assets shown in the
“Financial Highlights” section, which does not include acquired fund fees and expenses.2The portfolio’s investment adviser has contractually agreed to limit ordinary operating expenses (ordinary operating expenses means all portfolio expenses other than taxes, brokerage commissions,
acquired fund fees and expenses and extraordinary expenses, such as litigation) to the extent required to reduce expenses to 0.62% of the average daily net assets attributable to Class I shares. This expense
limitation is in effect through May 1, 2018. There can be no assurance that the adviser will extend the expense limitation beyond such time. Net expenses for a Class may exceed the applicable expense limitation to the
extent that the portfolio incurs excluded expenses. While in effect, the arrangement may be terminated only by agreement of the adviser and the Board of Trustees.




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Number of years you own your shares
(with or without redemption)13510Class I$64$217$383$864




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The market prices of securities held by the portfolio may go up or down, sometimes rapidly or unpredictably, due to general market conditions, such as real or perceived adverse economic,
political, or regulatory conditions, inflation, changes in interest or currency rates, lack of liquidity in the bond markets or adverse investor sentiment. In the past several years, financial markets, such as those
in the United States, Europe, Asia and elsewhere, have experienced increased volatility, depressed valuations, decreased liquidity and heightened uncertainty. These conditions may continue, recur, worsen or spread.
Events that have contributed to these market conditions include, but are not limited to, major cybersecurity events; measures to address U.S. federal and state budget deficits; downgrading of U.S. long-term sovereign
debt; declines in oil and commodity prices; dramatic changes in currency exchange rates; and public sentiment. The U.S. government and the Federal Reserve, as well as certain foreign governments and their central
banks, have taken steps to support financial markets. This and other government intervention may not work as intended, particularly if the efforts are perceived by investors as being unlikely to achieve the desired
results. The Federal Reserve has reduced its market support activities and recently has begun raising interest rates. Certain foreign governments and central banks are implementing or discussing so-called negative
interest rates (e.g., charging depositors who keep their cash at a bank) to spur economic growth. Further Federal Reserve or other U.S. or non-U.S. governmental or central bank actions, including interest rate
increases or contrary actions by different governments, could negatively affect financial markets generally, increase market volatility and reduce the value and liquidity of securities in which the portfolio invests.
Policy and legislative changes in the U.S. and in other countries are affecting many aspects of financial regulation, and may in some instances contribute to decreased liquidity and increased volatility in the
financial markets. The impact of these changes on the markets, and the practical implications for market participants, may not be fully known for some time. Economies and financial markets throughout the world are
increasingly interconnected. Economic, financial or political events, trading and tariff arrangements, terrorism, natural disasters and other circumstances in one country or region could have profound impacts on
global economies or markets. As a result, whether or not the portfolio invests in securities of issuers located in or with significant exposure to the countries directly affected, the value and liquidity of the
portfolio’s investments may be negatively affected. The portfolio may experience a substantial or complete loss on any individual security or derivative position.
 . Interest rates may go up, causing the value of the portfolio's investments to decline (this risk generally will be greater for securities with longer maturities or durations). For
example, if interest rates increase by 1%, the value of a fund’s portfolio with a portfolio duration of ten years would be expected to decrease by 10%, all other things being equal. Interest rates in the U.S.
recently have been historically low, so the portfolio faces a heightened risk that interest rates may rise. A general rise in interest rates may cause investors to move out of fixed income securities on a large scale,
which could adversely affect the price and liquidity of fixed income securities and could also result in increased redemptions from the portfolio. The maturity of a security may be significantly longer than its
effective duration. A security’s maturity may be more relevant than its effective duration in determining the security’s sensitivity to other factors such as changes in credit quality or in the yield
premium that the market may establish for certain types of securities.




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If an issuer or guarantor of a security held by the portfolio or a counterparty to a financial contract with the portfolio defaults on its obligation to pay principal and/or interest, has
its credit rating downgraded or is perceived to be less creditworthy, or the credit quality or value of any underlying assets declines, the value of your investment will typically decline.
 Many issuers have a right to prepay their securities. If interest rates fall, an issuer may exercise this right. If this happens, the portfolio will not benefit from the rise in market
price that normally accompanies a decline in interest rates, and will be forced to reinvest prepayment proceeds at a time when yields on securities available in the market are lower than the yield on the prepaid
security. The portfolio also may lose any premium it paid on the security.
 During periods of rising interest rates, the average life of certain types of securities may be extended because of slower than expected principal payments. This may lock in a below market
interest rate, increase the security's duration and reduce the value of the security.
 Some securities and derivatives held by the portfolio may be impossible or difficult to purchase, sell or unwind, particularly during times of market turmoil. An instrument’s
liquidity may be affected by reduced trading volume, a relative lack of market makers or legal restrictions, and illiquid securities and derivatives also may be difficult to value. Liquidity risk may be magnified in a
rising interest rate environment. If the portfolio is forced to sell an illiquid asset or unwind a derivatives position to meet redemption requests or other cash needs, the portfolio may be forced to sell at a loss.
The portfolio may not receive its proceeds from the sale of certain securities for an extended period (for example, several weeks or even longer). In extreme cases, this may constrain the portfolio’s ability to
meet its obligations (including obligations to redeeming shareholders).
 The adviser’s judgment about the quality, relative yield, relative value or market trends affecting a particular sector or region, market segment, security or about interest rates
generally may prove to be incorrect.
 The market value of direct obligations of the U.S. Treasury may vary due to changes in interest rates. In addition, changes to the financial condition or credit rating of the U.S.
government may cause the value of the portfolio’s investments in obligations issued by the U.S. Treasury to decline.
 The portfolio invests in obligations issued by agencies and instrumentalities of the U.S. government. Government-sponsored entities such as FNMA, FHLMC and the FHLBs, although chartered or
sponsored by Congress, are not funded by congressional appropriations and the debt and mortgage-backed securities issued by them are neither guaranteed nor issued by the U.S. government. The maximum potential
liability of the issuers of some U.S. government obligations may greatly exceed their current resources, including any legal right to support from the U.S. government. Such debt and mortgage-backed securities are
subject to the risk of default on the payment of interest and/or principal, similar to debt of private issuers. Although the U.S. government has provided financial support to FNMA and FHLMC in the past, there can be
no assurance that it will support these or other government-sponsored entities in the future.
 The value of mortgage-related and asset-backed securities will be influenced by factors affecting the housing market and the assets underlying such securities. As a result, during periods
of declining asset value, difficult or frozen credit markets, swings in interest rates, or deteriorating economic conditions, mortgage-related and asset-backed securities may decline in value, face valuation
difficulties, become more volatile and/or become illiquid. Mortgage-backed securities tend to be more sensitive to changes in interest rate than other types of debt securities. These securities are also subject to
prepayment and extension risks. Some of these securities may receive little or no collateral protection from the underlying assets and are thus subject to the risk of default. The risk of such defaults is generally
higher in the case of mortgage-backed investments that include so-called “sub-prime” mortgages. The structure of




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Certain debt instruments allow for balloon payments or negative amortization payments. Such instruments permit the borrower to avoid paying currently a portion of the interest accruing on
the instrument. While these features make the debt instrument more affordable to the borrower in the near term, they increase the risk that the borrower will be unable to make the resulting higher payment or payments
that become due at the maturity of the loan.
 Debt securities that are below investment grade, called “junk bonds,” are speculative, have a higher risk of default or are already in default, tend to be less liquid and are
more difficult to value than higher grade securities. Junk bonds tend to be volatile and more susceptible to adverse events and negative sentiments. These risks are more pronounced for securities that are already in
default.
 Floating rate loans and similar investments may be illiquid or less liquid than other investments and difficult to value. The value of collateral, if any, securing a floating rate loan can
decline or may be insufficient to meet the issuer’s obligations or may be difficult to liquidate. Market quotations for these securities may be volatile and/or subject to large spreads between bid and ask
prices. No active trading market may exist for many floating rate loans, and many loans are subject to restrictions on resale. Any secondary market may be subject to irregular trading activity and extended trade
settlement periods. In particular, loans may take longer than seven days to settle, potentially leading to the sale proceeds of loans not being available to meet redemptions for a substantial period of time after the
sale of the loans. To the extent that sale proceeds of loans are not available, the portfolio may sell securities that have shorter settlement periods or may access other sources of liquidity to meet redemption
requests. Loans may not be considered “securities,” and purchasers, such as the portfolio, therefore may not be entitled to rely on the anti-fraud protections afforded by federal securities laws.
 The return of principal and the payment of interest on “event-linked” bonds and other insurance-linked securities are contingent on the non-occurrence of a pre-defined
“trigger” event, such as a hurricane or an earthquake of a specific magnitude or other event that leads to physical or economic loss. If a trigger event, as defined within the terms of an event-linked
bond, involves losses or other metrics exceeding a specific magnitude in the geographic region and time period specified, the portfolio may lose a portion or all of its accrued interest and/or principal invested in
the event-linked bond. In addition to the specified trigger events, event-linked bonds may expose the portfolio to other risks, including but not limited to issuer (credit) default, adverse regulatory or
jurisdictional interpretations and adverse tax consequences. Certain insurance-linked securities may have limited liquidity, or may be illiquid. The portfolio has limited transparency into the individual contracts
underlying certain insurance-linked securities, which may make the risk assessment of such securities more difficult. Certain insurance-linked securities may be difficult to value.
 A holder of securities that are subordinated or “junior” to more senior securities of an issuer is entitled to payment after holders of more senior securities of the issuer.
Subordinated securities are more likely to suffer a credit loss than non-subordinated securities of the same issuer, any loss incurred by the subordinated securities is likely to be proportionately greater, and any
recovery of interest or principal may take more time. As a result, even a perceived decline in creditworthiness of the issuer is likely to have a greater impact on subordinated securities.
 The municipal bond market can be susceptible to unusual volatility, particularly for lower-rated and unrated securities. Liquidity can be reduced unpredictably in response to overall
economic conditions or credit tightening. Municipal issuers may be adversely affected by rising health care costs, increasing unfunded pension liabilities, and by the phasing out of federal programs providing
financial support.




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These securities may be more speculative and may fluctuate more in value than securities which pay income periodically and in cash. In addition, although the portfolio receives no periodic
cash payments on such securities, the portfolio is deemed for tax purposes to receive income from such securities, which applicable tax rules require the portfolio to distribute to shareholders. Such distributions may
be taxable when distributed to taxable shareholders.
 The market value of these transactions may increase or decrease as a result of changes in interest rates. These transactions involve risk of loss if the value of the underlying security
changes unfavorably before the settlement date or if the assets set aside to pay for these securities decline in value prior to the settlement date. Therefore, these transactions may have a leveraging effect on the
portfolio, making the value of an investment in the portfolio more volatile and increasing the portfolio’s overall investment exposure. There is also a risk that the other party to the transaction will default
on its obligation to purchase or sell the security, which may result in the portfolio missing the opportunity to obtain a favorable price or yield elsewhere.
 Investing in non-U.S. issuers, or in U.S. issuers that have significant exposure to foreign markets, may involve unique risks compared to investing in securities of U.S. issuers. These
risks are more pronounced for issuers in emerging markets or to the extent that the portfolio invests significantly in one region or country. These risks may include different financial reporting practices and
regulatory standards, less liquid trading markets, extreme price volatility, currency risks, changes in economic, political, regulatory and social conditions, terrorism, sustained economic downturns, financial
instability, tax burdens, and investment and repatriation restrictions. Lack of information and less market regulation also may affect the value of these securities. Withholding and other non-U.S. taxes may decrease
the portfolio’s return. Non-U.S. issuers may be located in parts of the world that have historically been prone to natural disasters. Investing in depositary receipts is subject to many of the same risks as
investing directly in non-U.S. issuers. Depositary receipts may involve higher expenses and may trade at a discount (or premium) to the underlying security. A number of countries in the European Union (EU) have
experienced, and may continue to experience, severe economic and financial difficulties. In addition, voters in the United Kingdom have approved withdrawal from the EU. Other countries may seek to withdraw from the EU
and/or abandon the euro, the common currency of the EU.
 The market values of convertible securities tend to decline as interest rates increase and, conversely, to increase as interest rates decline. A downturn in equity markets may cause the
price of convertible securities to decrease relative to other fixed income securities.
 Preferred stocks may pay fixed or adjustable rates of return. Preferred stocks are subject to issuer-specific and market risks applicable generally to equity securities. In addition, a
company’s preferred stocks generally pay dividends only after the company makes required payments to holders of its bonds and other debt. Thus, the value of preferred stocks will usually react more strongly than
bonds and




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The benefits to the portfolio from mortgage dollar roll transactions depend upon the adviser’s ability to forecast mortgage prepayment patterns on different mortgage pools. The
portfolio may lose money if, during the period between the time it agrees to the forward purchase of the mortgage securities and the settlement date, these securities decline in value due to market conditions or
prepayments on the underlying mortgages.
 Using swaps, futures and other derivatives can increase portfolio losses and reduce opportunities for gains when market prices, interest rates or the derivative instruments themselves
behave in a way not anticipated by the portfolio. Using derivatives may increase the volatility of the portfolio's net asset value and may not provide the result intended. Derivatives may have a leveraging effect on
the portfolio. Some derivatives have the potential for unlimited loss, regardless of the size of the portfolio’s initial investment. Changes in a derivative’s value may not correlate well with the
referenced asset or metric. The portfolio also may have to sell assets at inopportune times to satisfy its obligations. Derivatives may be difficult to sell, unwind or value, and the counterparty may default on its
obligations to the portfolio. Use of derivatives may have different tax consequences for the portfolio than an investment in the underlying security, and such differences may affect the amount, timing and character of
income distributed to shareholders. The U.S. government and foreign governments are in the process of adopting and implementing regulations governing derivatives markets, including mandatory clearing of certain
derivatives, margin and reporting requirements. The ultimate impact of the regulations remains unclear. Additional regulation of derivatives may make them more costly, may limit their availability, may disrupt markets
or may otherwise adversely affect their value or performance. In addition, the SEC has proposed a new rule that would change the regulation of the use of derivatives by registered investment companies, such as the
portfolio. If the proposed rule takes effect, it could limit the ability of the portfolio to invest in derivatives.
 Credit default swap contracts, a type of derivative instrument, involve special risks and may result in losses to the portfolio. Credit default swaps may in some cases be illiquid, and
they increase credit risk since the portfolio has exposure to the issuer of the referenced obligation and either the counterparty to the credit default swap or, if it is a cleared transaction, the brokerage firm
through which the trade was cleared and the clearing organization that is the counterparty to that trade.
 The interest rate on inverse floating rate obligations will generally decrease as short-term interest rates increase, and increase as short-term rates decrease. Due to their leveraged
structure, the sensitivity of the market value of an inverse floating rate obligation to changes in interest rates is generally greater than a comparable long-term bond issued by the same issuer and with similar
credit quality, redemption and maturity provisions. Inverse floating rate obligations may be volatile and involve leverage risk.
 The value of your investment may be more volatile and other risks tend to be compounded if the portfolio borrows or uses derivatives or other investments, such as ETFs, that have embedded
leverage. Leverage generally magnifies the effect of any increase or decrease in the value of the portfolio's underlying assets and creates a risk of loss of value on a larger pool of assets than the portfolio would
otherwise have, potentially resulting in the loss of all assets. Engaging in such transactions may cause the portfolio to liquidate positions when it may not be advantageous to do so to satisfy its obligations or meet
segregation requirements.
 In the event that the other party to a repurchase agreement defaults on its obligations, the portfolio may encounter delay and incur costs before being able to sell the security. Such a
delay may involve loss of interest or a decline in price of the security. In addition, if the portfolio is characterized by a court as an unsecured creditor, it would be at risk of losing some or all of the principal
and interest involved in the transaction.




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To the extent the portfolio emphasizes, from time to time, investments in a market segment, the portfolio will be subject to a greater degree to the risks particular to that segment, and
may experience greater market fluctuation than a portfolio without the same focus.
 If the portfolio does a lot of trading, it may incur additional operating expenses, which would reduce performance. A higher level of portfolio turnover may also cause taxable shareholders
to incur a higher level of taxable income or capital gains.
 The sales price the portfolio could receive for any particular portfolio investment may differ from the portfolio’s last valuation of the investment, particularly for illiquid
securities and securities that trade in thin or volatile markets or that are valued using a fair value methodology. Investors who purchase or redeem portfolio shares on days when the portfolio is holding fair-valued
securities may receive fewer or more shares or lower or higher redemption proceeds than they would have received if the portfolio had not fair-valued the securities or had used a different valuation methodology. The
portfolio’s ability to value its investments may also be impacted by technological issues and/or errors by pricing services or other third party service providers.
 The portfolio may experience heavy redemptions that could cause the portfolio to liquidate its assets at inopportune times or at a loss or depressed value, which could cause the value of
your investment to decline.
 Your actual costs of investing in the portfolio may be higher than the expenses shown in “Annual portfolio operating expenses” for a variety of reasons. For example, expense
ratios may be higher than those shown if overall net assets decrease. Net assets are more likely to decrease and portfolio expense ratios are more likely to increase when markets are volatile.




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1 Year5 Years10 YearsSince
Inception
(7/21/1987)Class I4.104.005.736.20Bloomberg Barclays U.S. Aggregate Bond Index (reflects no deduction for fees, expenses or taxes)2.652.234.346.47
  Investment adviserPioneer Investment Management, Inc.Portfolio managementKenneth J. Taubes, Executive Vice President and Chief Investment Officer, U.S. of Pioneer (portfolio manager of the portfolio since 2004); and Charles Melchreit, Senior Vice President
and Director of Investment Grade of Pioneer (portfolio manager of the portfolio since 2012)




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