UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED

MANAGEMENT INVESTMENT COMPANIES

Investment Company Act file number 811-21108

Pioneer Series Trust X

(Exact name of registrant as specified in charter)

60 State Street, Boston, MA 02109

(Address of principal executive offices) (ZIP code)

Terrence J. Cullen, Amundi Pioneer Asset Management, Inc.,

60 State Street, Boston, MA 02109

(Name and address of agent for service)

Registrant’s telephone number, including area code:  (617) 742-7825

Date of fiscal year end:  March 31, 2020

Date of reporting period: April 1, 2019 through March 31, 2020

Form N-CSR is to be used by management investment companies to file reports with the Commission not later than 10 days after the transmission to stockholders of any report that is required to be transmitted to stockholders under Rule 30e-1 under the Investment Company Act of 1940 (17 CFR 270.30e-1).  The Commission may use the information provided on Form N-CSR in its regulatory, disclosure review, inspection, and policymaking roles.

A registrant is required to disclose the information specified by Form N-CSR, and the Commission will make this information public. A registrant is not required to respond to the collection of information contained in Form N-CSR unless the Form displays a currently valid Office of Management and Budget (“OMB”) control number. Please direct comments concerning the accuracy of the information collection burden estimate and any suggestions for reducing the burden to Secretary, Securities and Exchange Commission, 450 Fifth Street, NW, Washington, DC 20549-0609.  The OMB has reviewed this collection of information under the clearance requirements of 44 U.S.C. ss. 3507.

 

Beginning in March 2021, as permitted by regulations adopted by the Securities and Exchange Commission, paper copies of the Fund’s shareholder reports like this one will no longer be sent by mail, unless you specifically request paper copies of the reports from the Fund or from your financial intermediary, such as a broker-dealer, bank or insurance company. Instead, the reports will be made available on the Fund’s website, and you will be notified by mail each time a report is posted and provided with a website link to access the report.

If you already elected to receive shareholder reports electronically, you will not be affected by this change and you need not take any action. You may elect to receive shareholder reports and other communications electronically by contacting your financial intermediary or, if you invest directly with the Fund, by calling 1-800-225-6292.

You may elect to receive all future reports in paper free of charge. If you invest directly with the Fund, you can inform the Fund that you wish to continue receiving paper copies of your shareholder reports by calling 1-800-225-6292. If you invest through a financial intermediary, you can contact your financial intermediary to request that you continue to receive paper copies of your shareholder reports. Your election to receive reports in paper will apply to all funds held in your account if you invest through your financial intermediary or all funds held within the Pioneer Fund complex if you invest directly.

visit us: www.amundipioneer.com/us

 

Pioneer Multi-Asset Ultrashort Income Fund | Annual Report | 3/31/20 1

Table of Contents

President’s Letter

Dear Shareholders,

The new decade has arrived delivering a first quarter that will go down in the history books. The beginning of the year seemed to extend the positive market environment of 2019 and then, March roared in like a lion and the COVID-19 pandemic became a global crisis impacting lives and life as we know it. The impact on the global economy from the COVID-19 virus pandemic, while currently unknown, is likely to be considerable. It is clear that several industries have already felt greater effects than others. And the markets, which do not thrive on uncertainty, have been volatile. Our business continuity plan was implemented given the new COVID-19 guidelines, and most of our employees are working remotely. To date, our operating environment has faced no interruption. I am proud of the careful planning that has taken place and confident we can maintain this environment for as long as is prudent. History in the making for a company that first opened its doors way back in 1928.

Since 1928, Amundi Pioneer’s investment process has been built on a foundation of fundamental research and active management, principles which have guided our investment decisions for more than 90 years. We believe active management – that is, making active investment decisions – can help mitigate the potential risks during periods of market volatility. As the early days of 2020 have reminded us, in today’s global economy, investment risk can materialize from a number of factors, including a slowing economy, changing U.S. Federal Reserve policy, oil price shocks, political and geopolitical factors and, unfortunately, major public health concerns such as a viral pandemic.

At Amundi Pioneer, active management begins with our own fundamental, bottom-up research process. Our team of dedicated research analysts and portfolio managers analyze each security under consideration, communicating directly with the management teams of the companies issuing the securities and working together to identify those securities that best meet our investment criteria for our family of funds. Our risk management approach begins with each and every security, as we strive to carefully understand the potential opportunity, while considering any and all risk factors.

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Today, as investors, we have many options. It is our view that active management can serve shareholders well, not only when markets are thriving, but also during periods of market stress. As you consider your long-term investment goals, we encourage you to work with your financial advisor to develop an investment plan that paves the way for you to pursue both your short-term and long-term goals.

We remain confident that the current crisis, like others in human history, will pass, and we greatly appreciate the trust you have placed in us and look forward to continuing to serve you in the future.

Sincerely,

Lisa M. Jones
Head of the Americas, President and CEO of U.S.
Amundi Pioneer Asset Management USA, Inc.
March 31, 2020

Any information in this shareowner report regarding market or economic trends or the factors influencing the Fund’s historical or future performance are statements of opinion as of the date of this report. Past performance is no guarantee of future results.

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Portfolio Management Discussion | 3/31/20

In the following interview, portfolio managers Seth Roman, Jonathan Sharkey, Noah Funderburk, and Nicolas Pauwels discuss the factors that influenced the performance of Pioneer Multi-Asset Ultrashort Income Fund during the 12-month period ended March 31, 2020. Mr. Roman, a vice president and a portfolio manager at Amundi Pioneer Asset Management, Inc. (Amundi Pioneer); Mr. Sharkey, a senior vice president and a portfolio manager at Amundi Pioneer; Mr. Funderburk, a vice president and a portfolio manager at Amundi Pioneer; and Mr. Pauwels, a vice president and a portfolio manager at Amundi Pioneer, are responsible for the day-to-day management of the Fund.

Q    How did the Fund perform during the 12-month period ended March 31, 2020?

A    Pioneer Multi-Asset Ultrashort Income Fund’s Class A shares returned -4.02% at net asset value (NAV) during the 12-month period ended March 31, 2020, while the Fund’s benchmark, the ICE Bank of America 3-Month U.S. Dollar LIBOR Index (the ICE BofA Index), returned 2.38%.

During the same period, the average return of the 204 mutual funds in Morningstar’s Ultrashort Bond category was 0.28%.

Q    Can you describe the market environment for fixed-income investors over the 12-month period ended March 31, 2020?

A    Entering the 12-month period, deteriorating global economic growth driven in part by the ongoing U.S.-China trade war was counterbalanced by the continued easing of global monetary policy. U.S. economic growth had held up better than growth in other developed markets during that timeframe, due to healthy consumer confidence data and continued strong employment figures. However, the plummeting manufacturing purchasing managers’ index (PMI) numbers, increased tariffs due to the U.S.-China trade dispute, and a downward trend in non-farm payrolls increased concerns about a U.S. recession. In particular, the on-again, off-again trade negotiations increased market volatility. Responding to those concerns, the U.S. Federal Reserve (Fed) followed up on its July 2019 rate cut with another quarter-point reduction in September. U.S. Treasury yields subsequently declined across the curve and fixed-income returns were buoyed by falling rates.

As the 12-month period drew to a close, the spread to pandemic levels of the COVID-19 virus from China to the rest of the world began to drive performance in the financial markets dramatically downward. Global economies ground to a near halt during March as public health concerns

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led to the rapid implementation by governments and companies of extreme measures focused on virus containment, including the shuttering of businesses deemed non-essential. Compounding the extreme market volatility and economic distress was the plummeting of oil prices to 20-year lows in response to slumping global demand resulting not only from the spread of COVID-19, but also from a supply shock spurred by a price war launched on March 8 between Saudi Arabia and Russia.

Uncertainty over the scope and duration of the pandemic crisis and the need for cash drove wholesale liquidations across most asset classes and a “flight-to-safety” trade that resulted in U.S. Treasury yields hitting historic lows. Significant selling in U.S. dollar (USD) fixed-income markets eventually stressed markets and led to price dislocations in all segments, even Treasury bonds.

Social-distancing and shelter-in-place measures enacted to help curb the spread of COVID-19 had profound economic effects and resulted in significant reductions in services consumption, manufacturing activity, construction, and labor demand. The unprecedented shutting down of much of the U.S. economy due to COVID-19 spurred extraordinary monetary and fiscal policy responses. The Fed jumped into action by dusting off its 2008/2009 policy “playbook” and rapidly rolling out a raft of programs aimed at restoring market liquidity, facilitating credit availability, and boosting investors’ confidence. The measures included reducing the benchmark federal funds rate to zero and committing to making unlimited purchases of U.S. Treasuries and agency mortgage-backed securities (MBS), if necessary, as well as providing support for commercial paper issuance, mutual fund liquidity needs, and the issuance of asset-backed securities (ABS). Additionally, the Fed entered uncharted waters with the announcement on March 23 of purchasing programs in support of investment-grade corporate bonds in both the new-issue and secondary markets. For its part, the U.S. government took steps to backstop the domestic economy with the passage of a stimulus bill in excess of $2 trillion, with the goal of assisting both individuals and businesses. Congressional leaders and the White House also were in discussions about possible further stimulus legislation as the 12-month period ended.

Selling pressures were most pronounced in the short-term markets relevant to most of the Fund’s investments. With “cash as king” in the latter part of the 12-month period, asset managers seeking to meet redemptions or redeploy capital into more deeply discounted securities flooded the market with short-term instruments. At its peak, the liquidity crisis witnessed the inversion of credit curves, with short-term corporates having higher

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spreads than longer-term corporates. (Credit spreads are commonly defined as the differences in yield between Treasuries and other types of fixed-income securities with similar maturities.)

Certain mutual funds began to receive large cash injections from their parents as they faced massive redemptions against the backdrop of a frozen commercial paper market. In turn, banks and broker/dealer balance sheets lacked the capacity to position the flood of assets, and so liquidity started to come at an increasingly high cost. Only the massive, $4 trillion (estimated) monetary stimulus by the Fed helped to restore confidence and liquidity to the market.

Among the U.S. bond market sectors, the liquidity stress was greatest in securitized credit, including ABS, commercial MBS (CMBS), and nonagency MBS, which have typically had a narrower buyer base than corporate bonds. Notably, while post-2008 crisis regulations have caused securitized sectors to offer compelling fundamental value, the same regulations have limited banks' ability to position those securities on their balance sheets, which has greatly exacerbated the price dislocations within the asset class. During the first calendar quarter of 2020, the ABS, MBS, and CMBS markets had to deal with forced selling by real estate investment trusts (REITs), other leveraged investors, and certain mutual funds, not to mention concerns about the impact of COVID-19 on employment and the corresponding ability of homeowners and businesses to pay their residential and commercial obligations.

Q    Can you review the Fund’s principal investment strategies during the 12-month period ended March 31, 2020, and how they affected benchmark-relative performance?

A    Investments in securitized sectors, where the portfolio is overweight compared to its peers, accounted for the majority of the Fund’s underperformance relative to the ICE BofA Index during the 12-month period. Exposures to collateralized mortgage obligations (CMOs), ABS, and CMBS were the primary detractors from benchmark-relative returns.

Within CMOs, the Fund’s allocation to credit-risk-transfer (CRT) securities, which transfer some of the risk of non-payment on residential mortgages from government-sponsored entities to the private sector, had the greatest negative effect on benchmark-relative performance for the 12-month period. Despite the recent underperformance, we believe we would have to experience a significant fall in home prices, similar to the declines of 2008, for the CRTs held by the portfolio to suffer permanent impairment. As a sector within non-agency MBS that has typically been

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more liquid, CRTs may have experienced greater price volatility from forced sellers over the month of March, compared with other segments of the non-agency MBS market.

Underperformance of the Fund’s CMBS holdings primarily reflected the struggles of the portfolio’s allocation to single-asset/single-borrower (SASB) investments. Each SASB securitization represents exposure to a single large property, or to the assets of a single borrower, and can include exposure to collateral such as office towers, suburban office parks, apartment buildings, refrigerated warehouses, and hotels. Because of the concentrated risk, SASBs have tended to feature conservative loan-to-value ratios compared to traditional CMBS instruments. In addition, equity owners of those properties have tended to be well-capitalized firms. The portfolio’s allocation to commercial real estate collateralized loan obligations (CLOs) also detracted from the Fund’s benchmark-relative returns during the 12-month period.

Another detractor from the Fund’s relative returns were its ABS positions backed by consumer loans – where the portfolio’s investments have resided primarily in the most senior tranches – and AAA-rated credit card collateral. At the peak of March's distress and volatility, credit card ABS spreads had widened to historical extremes due to market illiquidity and concerns about consumer delinquencies in the wake of the COVID-19 crisis. We believe the launch of the Fed’s Term Asset-Backed Securities Loan Facility (TALF), expected in early May, could enable purchases of new-issue AAA-rated ABS, and thereby help to restore liquidity to the market.

Other portfolio allocations that had negative effects on the Fund’s benchmark-relative performance during the 12-month period included corporate credit holdings within the financials and industrials sectors, and holdings of bank loans.

Positive contributions to the Fund’s benchmark-relative returns during the 12-month period were led by an allocation to insurance-linked securities (ILS), which are sponsored by property-and-casualty insurers seeking to mitigate the effects of having to pay claims in the wake of natural disasters. The ostensibly exotic ILS market, which has typically had little or no correlation to other financial markets, proved to have relatively resilient liquidity during the extremely volatile market environment we experienced during the first calendar quarter of 2020. ILS had also displayed similar resiliency during the global financial crisis almost 12 years ago.

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Q    Can you discuss the factors that affected the Fund’s income-generation/ distributions* to shareholders, either positively or negatively, during the 12-month period ended March 31, 2020?

A    Throughout the period, we had invested the Fund in floating-rate issues with interest rates tied to London Interbank Offered Rates (LIBOR), or other short-term reference rates. The Fund’s income remained quite steady over the 12-month period, despite a decline in short-term LIBOR rates.

Historically, changes to the Fund’s dividend yield have tended to lag changes in LIBOR rates.

Q    Did the Fund have any exposure to derivatives during the 12-month period ended March 31, 2020?

A    No, the Fund had no derivatives exposure during the 12-month period.

Q    What is your assessment of the current investment environment in the fixed-income markets, and how have you positioned the portfolio for that environment?

A    Entering the Fund’s new fiscal year, we have continued to hold significant exposure to securitized credit within the portfolio. As noted previously, the sector suffered late in the 12-month period due to concerns about liquidity and fundamentals, with the latter focused on the ability of U.S. consumers to remain current on their credit card, auto, and home payments, and of businesses to pay their rents. With that said, on the consumer side, we believe securitized credit may benefit from consumers’ markedly higher aggregate savings rates, record levels of total wealth, and significantly lower levels of leverage compared with 2008. In general, relative to 2008, we believe the securitized credit market reflects much stronger underwriting standards, with greater risk-retention by issuers, more stringent rating-agency standards, and much higher levels of credit protection. In recalibrating credit protections, the rating agencies have sought to ensure that investment-grade-rated MBS issues would not suffer permanent impairment when facing a downside scenario such as occurred in 2008. It is important to note that, in the overvalued market of 2008, home prices eventually declined by approximately 30%, and commercial real estate prices declined by approximately 40%. We believe that both residential and commercial real estate valuations are much more reasonable than they were in those days and that, while there are no guarantees, neither housing nor commercial real estate should suffer the dramatic declines experienced during the 2008/09 financial crisis.

*  Distributions and dividend yields are not guaranteed.

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Given currently wide credit spreads, we believe that corporate credit offers attractive investment opportunities. We believe the wider spreads for investment-grade corporates have resulted primarily from the aforementioned liquidity squeeze, rather than from fundamental factors. In addition, the Fund’s management team believes the financial sector, particularly U.S. and European banks, has continued to offer value. Banks have significantly improved their balance sheets and capital positions over the past several years, and have been subject to increased regulatory oversight.

The Fund’s current positioning is designed to allow it to possibly benefit from any potential recovery in credit markets. With investment-grade corporate spreads well above their long-term average, we believe investors have been receiving fair compensation for taking on credit risk. As the year progresses, we think we could see further spread compression should the global economy begin to recover.

Importantly, we do not believe the Fund faces any material, permanent impairment of capital in the current difficult environment. Given the greater credit sensitivity of the portfolio relative to the benchmark ICE BofA Index, we believe the Fund has the potential to generate solid benchmark-relative performance over the longer term.

Please refer to the Schedule of Investments on pages 21–89 for a full listing of Fund securities.

All investments are subject to risk, including the possible loss of principal. In the past several years, financial markets have experienced increased volatility and heightened uncertainty. The market prices of securities 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, recessions, inflation, changes in interest or currency rates, lack of liquidity in the bond markets, the spread of infectious illness or other public health issues or adverse investor sentiment. These conditions may continue, recur, worsen or spread.

The Fund has the ability to invest in a wide variety of debt securities.

The Fund may invest in underlying funds (including ETFs). In addition to the Fund’s operating expenses, you will indirectly bear the operating expenses of investments in any underlying funds.

The Fund and some of the underlying funds may utilize strategies that have a leveraging effect on the Fund, which increases the volatility of investment returns and subjects the Fund to magnified losses if the Fund’s or an underlying fund’s investments decline in value.

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The Fund and some of the underlying funds may use derivatives, such as options and futures, which can be illiquid, may disproportionately increase losses, and have a potentially large impact on Fund performance.

The Fund may invest in inflation-linked securities. As inflationary expectations increase, inflation-linked securities may become more attractive, because they protect future interest payments against inflation. Conversely, as inflationary concerns decrease, inflation-linked securities will become less attractive and less valuable.

The Fund may invest in credit default swaps, which may in some cases be illiquid, and they increase credit risk since the Fund has exposure to both the issuer of the referenced obligation and the counterparty to the credit default swap.

The Fund may invest in subordinated securities which may be disproportionately adversely affected by a default or even a perceived decline in creditworthiness of the issuer.

The Fund may invest in floating-rate loans. 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.

The Fund may invest in insurance-linked securities. The return of principal and the payment of interest and/or dividends on 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.

The Fund may invest in zero-coupon bonds and payment-in-kind securities, which may be more speculative and fluctuate more in value than other fixed income securities. The accrual of income from these securities are payable as taxable annual dividends to shareholders.

Investments in equity securities are subject to price fluctuation.

International investments are subject to special risks including currency fluctuations, social, economic and political uncertainties, which could increase volatility. These risks are magnified in emerging markets.

Investments in fixed-income securities involve interest rate, credit, inflation, and reinvestment risks. As interest rates rise, the value of fixed income securities generally falls.

The Fund may invest in mortgage-backed securities, which during times of fluctuating interest rates may increase or decrease more than other fixed-income securities. Mortgage-backed securities are also subject to pre-payments.

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Prepayment risk is the chance that an issuer may exercise its right to prepay its security, if falling interest rates prompt the issuer to do so. Forced to reinvest the unanticipated proceeds at lower interest rates, the Fund would experience a decline in income and lose the opportunity for additional price appreciation.

High yield bonds possess greater price volatility, illiquidity, and possibility of default.

There may be insufficient or illiquid collateral securing the floating rate loans held within the Fund. This may reduce the future redemption or recovery value of such loans.

The Fund may have disadvantaged access to confidential information that could be used to assess a loan issuer, as Amundi Pioneer normally seeks to avoid receiving material, non-public information.

The Fund is not a money market fund.

These risks may increase share price volatility.

There is no assurance that these and other strategies used by the Fund or underlying funds will be successful.

Please see the prospectus for a more complete discussion of the Fund’s risks.

Before investing, consider the product’s investment objectives, risks, charges and expenses. Contact your advisor or Amundi Pioneer Asset Management, Inc., for a prospectus or summary prospectus containing this information. Read it carefully.

Any information in this shareholder report regarding market or economic trends or the factors influencing the Fund’s historical or future performance are statements of opinion as of the date of this report. Past performance is no guarantee of future results.

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