Harbor Multi-Asset Total Return ETF Summary Prospectus

Harbor Multi-Asset Total Return ETF (formerly, Harbor Multi-Asset Explorer ETF)

MATR

Summary Prospectus – March 1, 2026 (as amended August 31, 2026)

Before you invest, you may want to review the Fund’s prospectus, which contains more information about the Fund and its risks. You can find the Fund’s prospectus and other information about the Fund online at harborcapital.com/prospectus. You can also get this information at no cost by calling 800-422-1050 or by sending an email request to funddocuments@harborcapital.com. If you purchase shares of the Fund through a financial intermediary, the prospectus and other information will also be available from your financial intermediary. The current prospectus and statement of additional information, dated March 1, 2026, as amended or supplemented from time to time, are incorporated by referenced into this summary prospectus and may be obtained, free of charge, at the website, phone number or email address noted above.

Investment Objective

The Fund seeks to provide long-term total return while limiting downside risk.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy, hold and sell shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and example below.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

	Rate
Management Fees	0.70%
Distribution and Service (12b-1) Fees	None
Other Expenses1	0.00%
Acquired Fund Fees and Expenses2	0.10%
Total Annual Fund Operating Expenses	0.80%

1 Pursuant to the Investment Advisory Agreement, the Advisor pays all of the operating expenses of the Fund (inclusive of any expenses of a wholly owned subsidiary of the Fund), except for (i) the fee payment under the Investment Advisory Agreement; (ii) payments under the Fund’s 12b-1 plan (if any); (iii) the costs of borrowing, including interest and dividend expenses; (iv) taxes and governmental fees; (v) acquired fund fees and expenses; (vi) brokers’ commissions and any other transaction-related expenses and fees arising out of transactions effected on behalf of the Fund; (vii) costs of holding shareholder meetings; and (viii) litigation and indemnification expenses and other extraordinary expenses not incurred in the ordinary course of the Fund’s business.

2 Estimated for the current fiscal year.

Expense Example

This Expense Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other exchange-traded funds. The Expense Example assumes that you invest $10,000 in the Fund for the time periods indicated. The Expense Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, under these assumptions, your costs would be:

	One Year	Three Years	Five Years	Ten Years
ETF	$82	$255	$444	$990

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when shares of the Fund are held in a taxable account. These costs, which are not reflected in the Annual Fund

Operating Expenses or in the Expense Example, do affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 155%. Portfolio turnover rate excludes investments received or delivered from in-kind processing of creation unit purchases or redemptions.

Principal Investment Strategy

To seek to achieve the Fund’s investment objective, Harbor Capital Advisors Inc., the Fund’s investment adviser (the “Advisor”), allocates the Fund’s assets among various asset classes and market sectors based on its assessment of global economic and market conditions, primarily through investments in a diversified portfolio of exchange-traded funds, including other funds managed by the Advisor (“Underlying Funds”).

The Fund invests in Underlying Funds that provide exposure to one or more broad asset classes that include equities (including the common stock of issuers of all capitalizations), fixed income securities of any credit quality (including below-investment grade bonds, also known as high-yield bonds or “junk” bonds), real estate investment trusts that provide exposure to the broad real estate market, commodities (primarily gold), U.S. government securities and cash. The Fund invests, through Underlying Funds, in markets around the world, including both in developed and emerging markets. The Fund primarily invests in Underlying Funds that seek to track indices, including those designed to provide exposure to particular sectors or industries (such as communication services, financials and/or technology) or style factors (such as growth, value, and/or low volatility). However, the Fund may invest in Underlying Funds that are actively managed. While the Fund primarily invests through Underlying Funds, it may also invest directly in equity and fixed income securities and futures in limited circumstances where the Advisor believes that a particular exposure is better achieved through direct investments. As discussed further below, the Fund may invest in derivatives through the Subsidiary (as defined below) to obtain the Fund’s intended exposure to commodities. The Fund’s indirect and direct investments may be in the securities of foreign and emerging market issuers, which may be denominated in currencies other than the U.S. dollar.

The Advisor’s broad-based approach to managing the Fund combines both systematic and discretionary research and analysis. In managing the Fund, the Advisor seeks to understand the economic and business cycle, and the risks and opportunities the current cycle presents using its proprietary multi-factor model that includes growth, liquidity, and inflation factors (the “model”). The model categorizes the business cycle into various regimes based primarily on the intersection of these three macro factors – growth, liquidity, and inflation – using a probabilistic approach to assess the future state of these factors. The Fund employs an asset allocation strategy driven by regime modeling, which seeks to capture upside during risk-friendly business cycle regimes and preserve capital in risk-averse regimes. The Fund utilizes a four-step process that involves: (1) regime identification; (2) return estimation; (3) portfolio construction; and (4) qualitative review.

Step 1 – Regime Identification. The Advisor utilizes the output of the systematic model to determine the prevailing business cycle

Summary Prospectus

Harbor Multi-Asset Total Return ETF (formerly, Harbor Multi-Asset Explorer ETF)

regime. Within the model, growth factors are used to measure economic growth conditions; liquidity factors are used to measure the credit cycle; and inflation factors are used to measure the direction of trend inflation. The identification of the prevailing business cycle regime determines the risk parameters and general asset allocation for the Fund.

Step 2 – Return Estimation. The Advisor’s model systematically generates return estimates for a population of assets reflecting global equities, credit, core bonds, currencies, and commodities.

Step 3 – Portfolio Construction. The Advisor conducts various portfolio optimizations using estimates for risk, correlation and returns, targeting the portfolio risk parameters identified as described in step 1 and using the returns identified in step 2.

Step 4 – Qualitative Review of the Fund’s Portfolio. The Advisor adjusts portfolio positions to reflect discretionary analysis, including, but not limited to, valuation, sentiment, and sector fundamentals. The Fund’s portfolio managers balance the optimal portfolio identified solely based upon the systematic model against the opportunities identified through their discretionary analysis, subject to controlled ranges for deviation from the optimized portfolio in terms of relative volatility and tracking error. (Tracking error is a measure of the risk in an investment portfolio that is due to active management decisions.) The Advisor is also permitted to make broader changes to the asset allocation suggested by the systematic model but expects to do so only in limited situations. The resulting portfolio is then implemented by the Advisor by investing the Fund’s assets primarily in Underlying Funds.

Because the Fund’s targeted risk is largely determined by the systematically identified regime, the Fund’s portfolio may at times be positioned defensively during risk-averse regimes. This may help the Fund’s portfolio to preserve capital during drawdowns. However, if assets such as equities and credit perform well during a risk-averse regime when the Fund’s portfolio is defensively positioned, the Fund’s portfolio may underperform relative to the broader market.

In order to facilitate the Fund’s exposure to commodities, the Fund will invest up to 25% of its total assets, as determined at the end of each fiscal quarter, in a wholly owned and controlled subsidiary (the “Subsidiary”) organized under the laws of the Cayman Islands. The Fund’s investment in the Subsidiary is expected to provide the Fund with exposure to commodity returns within the limits of the federal tax laws, which limit the ability of investment companies such as the Fund to invest directly in such instruments. The Subsidiary has the same investment objective and will follow the same investment policies and restrictions as the Fund, with the exception that the Subsidiary may invest without limitation in exchange-traded products backed by or linked to a physical commodity or commodity-linked derivative instruments. The Subsidiary’s investment in derivative instruments, including excess return swaps and futures, may have a leveraging effect on the Fund because of the leverage inherent in the use of derivatives. References to the Fund’s investment strategies and risks include those of its Subsidiary. The Subsidiary is advised by the Advisor.

The Advisor may sell a holding if the Advisor’s outlook on an asset class or sector changes or the Advisor identifies what it believes to be a more attractive investment opportunity. The portfolio will generally be rebalanced on a monthly basis, although the Advisor reserves the right to rebalance the portfolio at other times in response to market conditions.

The Fund has wide flexibility in the relative weightings of asset classes and sectors and the Fund’s asset allocation can change significantly over time based on the Advisor’s outlook for the global economy and market conditions. The Fund may at times engage

in active and frequent trading to achieve its principal investment strategies.

Principal Risks

There is no guarantee that the investment objective of the Fund will be achieved. The Fund’s share price fluctuates and the value of your investment in the Fund may go down. This means that you could lose money on your investment in the Fund or the Fund may not perform as well as other investment options. Principal risks impacting the Fund (in alphabetical order after the first four risks) include those set forth below. The following risks include the principal risks that the Fund is exposed to through its direct investments in securities and other instruments as well as through its investments in Underlying Funds:

ETF Risk: The Fund’s investment in shares of ETFs subjects it to the risks of owning the securities underlying the ETF, as well as the same structural risks faced by an investor purchasing shares of the Fund, including premium/discount risk and authorized participant concentration/trading risk. As a shareholder in another ETF, the Fund bears its proportionate share of the ETF’s expenses.

Asset Allocation Risk: The Fund’s investment performance depends upon the successful allocation by the Advisor of the Fund’s assets among asset classes, geographical regions, sectors and specific investments. The Advisor’s judgment about the attractiveness, value and growth potential of a particular asset class, region, sector or investment may be incorrect and the Advisor’s selection of the Underlying Funds to implement its asset allocation decisions may not produce the desired results. The Advisor potentially will be prevented from executing investment decisions at an advantageous time or price as a result of domestic or global market disruptions, particularly disruptions causing heightened market volatility and reduced market liquidity, as well as increased or changing regulations.

Market Risk: Securities markets are volatile and can decline significantly in response to adverse market, economic, political, regulatory or other developments, which may lower the value of securities held by the Fund, sometimes rapidly or unpredictably. Events such as war, military conflict, geopolitical disputes, acts of terrorism, social or political unrest, natural disasters, recessions, inflation, rapid interest rate changes, supply chain disruptions, tariffs and other restrictions on trade, sanctions, the spread of infectious illness or other public health threats, or the threat or potential of one or more such events and developments, could also significantly impact the Fund and its investments.

Risks Associated with Exchange-Traded Funds: As an ETF, the Fund is subject to the following risks:

Authorized Participant Concentration/Trading Risk: Only authorized participants (“APs”) may engage in creation or redemption transactions directly with the Fund. The Fund has a limited number of institutions that may act as APs and such APs have no obligation to submit creation or redemption orders. Consequently, there is no assurance that APs will establish or maintain an active trading market for the shares. This risk may be heightened to the extent that securities held by the Fund are traded outside a collateralized settlement system. In that case, APs may be required to post collateral on certain trades on an agency basis (i.e., on behalf of other market participants), which only a limited number of APs may be able to do. In addition, to the extent that APs exit the business or are unable to proceed with creation and/or redemption orders with respect to the Fund and no other AP is able to step forward to create or redeem Creation Units (as defined below), this may result in a significantly diminished trading market for shares, and shares may be more likely to trade

Summary Prospectus

Harbor Multi-Asset Total Return ETF (formerly, Harbor Multi-Asset Explorer ETF)

at a premium or discount to the Fund’s net asset value and to face trading halts and/or delisting. This risk may be heightened during periods of volatility or market disruptions.

Cash Transactions Risk: The Fund may effect some or all of its creations and redemptions for cash rather than in-kind. As a result, an investment in the Fund may be less tax-efficient than an investment in an ETF that effects all of its creations and redemptions in-kind. Because the Fund may effect redemptions for cash, it may be required to sell portfolio securities in order to obtain the cash needed to distribute redemption proceeds. A sale of portfolio securities may result in capital gains or losses and may also result in higher brokerage costs. To the extent costs are not offset by transaction fees charged by the Fund to APs, the costs of cash transactions will be borne by the Fund.

Premium/Discount Risk: The market price of the Fund’s shares will generally fluctuate in accordance with changes in the Fund’s net asset value as well as the relative supply of and demand for shares on the Exchange. The Advisor cannot predict whether shares will trade below, at or above their net asset value because the shares trade on the Exchange at market prices and not at net asset value. Price differences may be due, in large part, to the fact that supply and demand forces at work in the secondary trading market for shares will be closely related, but not identical, to the same forces influencing the prices of the holdings of the Fund trading individually or in the aggregate at any point in time. This may result in the Fund’s shares trading significantly above (premium) or below (discount) the Fund’s net asset value, which will be reflected in the intraday bid/ask spreads and/or the closing price of shares as compared to net asset value. However, given that shares can only be purchased and redeemed in Creation Units to and from broker-dealers and large institutional investors that have entered into participation agreements (unlike shares of closed-end funds, which frequently trade at appreciable discounts from, and sometimes at premiums to, their net asset value), the Advisor believes that large discounts or premiums to the net asset value of shares should not be sustained. During stressed market conditions, the market for the Fund’s shares may become less liquid in response to deteriorating liquidity in the market for the Fund’s underlying portfolio holdings, which could in turn lead to differences between the market price of the Fund’s shares and their net asset value.

Affiliated Fund Risk: The Advisor is subject to potential conflicts of interest in determining whether to invest in an underlying fund managed by the Advisor, and the Advisor may have an economic or other incentive to make or retain an investment in an affiliated fund in lieu of other investments that may also be appropriate for the Fund.

Commodity Risk: Commodity prices are generally affected by, among other factors, the cost of producing, transporting and storing commodities, changes in consumer or commercial demand for commodities, the hedging and trading strategies of producers and consumers of commodities, speculative trading in commodities by commodity pools and other market participants, disruptions in commodity supply, weather, political and other global events, global economic factors and government intervention in or regulation of the commodity or commodity futures markets. The prices of individual commodities may be volatile and the values of commodity-related ETFs and derivatives may be highly sensitive to the price of those commodities. To the extent the Fund has exposure to a single commodity (such as gold), it will be more susceptible to the risks associated with that particular commodity.

Commodity-Linked Derivatives Risk: The Fund’s investments in commodity-linked derivative instruments (either directly or through the Subsidiary) may subject the Fund to significantly greater volatility than investments in traditional securities. The value of

commodity-linked derivative instruments may be affected by prevailing spot prices (the price at which a commodity can be bought or sold for immediate delivery) for the underlying commodity, supply and demand, market activity, liquidity, economic, financial, political regulatory, geographical, biological or judicial events, and the general interest rate environment. Commodity-linked derivatives are subject to the risk that the counterparty to the transaction, the exchange or trading facility on which they trade, or the applicable clearing house may default or otherwise fail to perform. The Fund will incur certain costs as a result of its use of derivatives and is required to post margin in respect to certain of its holdings in derivatives. Costs incurred by the Fund as a result of its use of derivatives will ultimately be borne by shareholders.

The Fund’s use of commodity-linked derivatives will have a leveraging effect on the Fund’s portfolio. Leverage generally magnifies the effect of a change in the value of an asset and creates a risk of loss of value on a larger pool of assets than the Fund otherwise would have had. The Fund’s exposure to leverage can substantially increase the adverse impact to which the Fund’s investment portfolio may be subject and make the Fund more volatile.

Credit Risk: The issuer or guarantor of a security owned by the Fund could default on its obligation to pay principal or interest or its credit rating could be downgraded. Likewise, a counterparty to a derivative or other contractual instrument owned by the Fund could default on its obligation. This risk may be higher for below investment-grade securities.

Derivatives Risk: The value of derivative instruments held by the Fund or to which the Fund has exposure may not change in the manner expected by the Subadvisor and/or Advisor, as applicable,, which could result in disproportionately large losses to the Fund. Derivative instruments are subject to the following risks: (i) leverage (the risk that derivatives transactions can magnify the fund’s gains and losses); (ii) market (the risk from potential adverse market movements in relation to the Fund’s derivatives positions, or the risk that markets could experience a change in volatility that adversely impacts fund returns and the Fund’s obligations and exposures); (iii) counterparty (the risk that a counterparty on a derivatives transaction may not be willing or able to perform its obligations under the derivatives contract, and the related risks of having concentrated exposure to such a counterparty); (iv) liquidity (the risk involving the liquidity demands that derivatives can create to make payments of margin, collateral, or settlement payments to counterparties), (v) operational (the risk related to potential operational issues, including documentation issues, settlement issues, systems failures, inadequate controls, and human error); and (vi) legal (the risk of insufficient documentation, insufficient capacity or authority of counterparty, or legality or enforceability of a contract). Derivatives may also be more volatile than other instruments and may create a risk of loss greater than the amount invested. In addition, certain derivatives may be difficult to value and may be illiquid.

Emerging Market Risk: Because the Fund may invest in securities of emerging market issuers, an investment in the Fund may be subject to special risks in addition to those of U.S. securities. These risks include heightened political and economic risks, greater volatility, currency fluctuations, higher transaction costs, delayed settlement, possible foreign controls on investment, possible sanctions by governmental bodies of other countries and less stringent investor protection and disclosure standards of foreign markets. Foreign securities are sometimes less liquid and harder to value than securities of U.S. issuers. The securities markets of many foreign countries are relatively small, with a limited number

Summary Prospectus

Harbor Multi-Asset Total Return ETF (formerly, Harbor Multi-Asset Explorer ETF)

of companies representing a small number of industries. If foreign securities are denominated and traded in a foreign currency, the value of the Fund’s foreign holdings can be affected by currency exchange rates and exchange control regulations. The Fund’s investments in foreign securities may also be subject to foreign withholding taxes.

Foreign securities risks are more significant in emerging market countries. These countries may have relatively unstable governments and less-established market economies than developed countries. Emerging markets may face greater social, economic, regulatory and political uncertainties. These risks make emerging market securities more volatile and less liquid than securities issued in more developed countries. Securities exchanges in emerging markets may suspend listed securities from trading for substantially longer periods of time than exchanges in developed markets, including for periods of a year or longer. If the Fund is holding a suspended security, that security would become completely illiquid as the Fund would not be able to dispose of the security until the suspension is lifted. In such instances, it can also be difficult to determine an appropriate valuation for the security because of a lack of trading and uncertainty as to when trading may resume.

Global economies and financial markets are becoming increasingly interconnected, and conditions and events in one country, region or financial market may adversely impact issuers in a different country, region or financial market.

Equity Risk: The values of equity securities may decline due to general market conditions that are not specifically related to a particular company, such as real or perceived adverse economic conditions, changes in the general outlook for corporate earnings, changes in interest or currency rates or adverse investor sentiment generally. They may also decline due to factors that affect a particular industry or industries, such as labor shortages or increased production costs and competitive conditions within an industry. Equity securities generally have greater price volatility than fixed income securities.

Fixed Income Security Risk: Fixed income securities fluctuate in price in response to various factors, including changes in interest rates, changes in market conditions and issuer-specific events.

Foreign Currency Risk: As a result of the Fund’s investments in securities denominated in, and/or receiving revenues in, foreign currencies, the Fund will be subject to currency risk. Currency risk is the risk that foreign currencies will decline in value relative to the U.S. dollar or, in the case of hedging positions, that the U.S. dollar will decline in value relative to the currency hedged. In either event, the dollar value of an investment in the Fund would be adversely affected.

Foreign Securities Risk: Because the Fund may invest in securities of foreign issuers, an investment in the Fund is subject to special risks in addition to those of U.S. securities. These risks include heightened political and economic risks, greater volatility, currency fluctuations, higher transaction costs, delayed settlement, possible foreign controls on investment, possible sanctions by governmental bodies of other countries and less stringent investor protection and disclosure standards of foreign markets. Foreign securities are sometimes less liquid and harder to value than securities of U.S. issuers. These risks are more significant for issuers in emerging market countries. Global economies and financial markets are becoming increasingly interconnected, and conditions and events in one country, region or financial market may adversely impact issuers in a different country, region or financial market.

High Portfolio Turnover Risk: Higher portfolio turnover may adversely affect Fund performance by increasing Fund transaction costs and may lead to the realization and distribution to shareholders

of higher capital gains, which may increase a shareholder’s tax liability.

High-Yield Risk: There is a greater risk that the Fund will lose money because it invests in below investment-grade fixed income securities and unrated securities of similar credit quality (commonly referred to as “high-yield” or “junk” bonds). These securities are considered speculative because they have a higher risk of issuer default, are subject to greater price volatility and may be illiquid.

Issuer Risk: An adverse event affecting a particular issuer in which the Fund is invested, such as an unfavorable earnings report, may depress the value of that issuer’s securities, sometimes rapidly or unpredictably.

Large Shareholder Risk: Certain large shareholders including authorized participants (“AP”), third-party investors, the Advisor, affiliates of the Advisor, market makers, or other entities, including funds or accounts over which the Advisor, an affiliate of the Advisor or a third-party intermediary has investment discretion, such as those investing through one or more model portfolios, may from time to time own or control a substantial amount of the Fund’s shares. There is no requirement that these shareholders maintain their investment in the Fund. There is a risk that such large shareholders or that the Fund’s shareholders generally may redeem all or a substantial portion of their investments in the Fund in a short period of time, including as a result of an asset allocation decision made by the Advisor, an affiliate of the Advisor or a third-party intermediary, which could have a significant negative impact on the Fund’s NAV, liquidity, and brokerage costs. Large redemptions could also result in tax consequences to shareholders and impact the Fund’s ability to implement its investment strategy. In addition, transactions by large shareholders may account for a large percentage of the trading volume on the listing exchange and may, therefore, have a material upward or downward effect on the market price of the shares.

Mortgage- and Asset-Backed Securities Risk: Mortgage and other asset-backed securities are subject to credit, interest rate, extension, prepayment, and other risks. For mortgage and other asset-backed securities in the Fund’s portfolio that have embedded leverage, small changes in interest or prepayment rates may cause large and sudden price movements.

New Fund Risk: There can be no assurance that the Fund will grow to or maintain an economically viable size, in which case the Board of Trustees may determine to liquidate the Fund. The Board of Trustees may liquidate the Fund at any time in accordance with the Declaration of Trust and governing law. As a result, the timing of the Fund’s liquidation may not be favorable.

Market Capitalization Risk: The Fund may invest in companies of any market capitalization. Securities of smaller companies are usually less stable in price and less liquid than those of larger, more established companies. Smaller companies may have limited product lines, markets and financial resources. Additionally, small- and mid-cap stocks may fall out of favor relative to large cap stocks, which may cause the Fund to underperform other equity funds that focus on larger capitalized companies. Likewise, large cap stocks may fall out of favor relative to small- and mid-cap stocks, which may cause the Fund to underperform other equity funds that focus on smaller capitalized companies.

Quantitative Analysis Risk: There are limitations inherent in every quantitative model. The value of securities selected using quantitative analysis can react differently to issuer, political, market, and economic developments than the market as a whole or securities selected using only fundamental analysis. The factors used in quantitative analysis and the weight placed on those factors may not be predictive of a security’s value. In addition, historical trends

Summary Prospectus

Harbor Multi-Asset Total Return ETF (formerly, Harbor Multi-Asset Explorer ETF)

in data may not be predictive going forward. The strategies and techniques employed in a quantitative model cannot fully match the complexity of the financial markets and therefore sudden unanticipated changes in underlying market conditions can significantly impact their performance. The effectiveness of the given strategy or technique may deteriorate in an unpredictable fashion for any number of reasons including, but not limited to, an increase in the amount of assets managed or the use of similar strategies or techniques by other market participants and/or market dynamic shifts over time. In addition, factors that affect a security’s value can change over time, and these changes may not be reflected in the quantitative model. Any model may contain flaws the existence and effect of which may be discovered only after the fact or not at all. There can be no assurances that the strategies pursued or the techniques implemented in the quantitative model will be profitable, and various market conditions may be materially less favorable to certain strategies than others. Even in the absence of flaws, a model may not perform as anticipated.

Precious Metals Investment Risk: Prices of precious metals, including gold and silver, and of precious metal-related financial instruments historically have been very volatile and may fluctuate sharply over short periods of time. The high volatility of precious metals prices may adversely affect the prices of financial instruments that derive their value from the price of underlying precious metals. The production and sale of precious metals by governments or central banks or other larger holders can be affected by various economic, financial, social and political factors, which may be unpredictable and may have a significant impact on the prices of precious metals.

REIT Risk: REITs in which the Fund invests may decline in value as a result of factors affecting the real estate sector, such as changes in real estate values, changes in property taxes and government regulation affecting zoning, land use and rents, changes in interest rates, changes in the cash flow of underlying real estate assets, levels of occupancy, and market conditions, as well as the management skill and creditworthiness of the issuer. Investments in REITs are also subject to additional risks, including the risk that REITs are unable to generate cash flow to make distributions to unitholders and fail to qualify for favorable tax treatment under the Internal Revenue Code of 1986, as amended.

Sector Risk: To the extent that the Fund has significant exposure to a particular sector or commodity, the Fund will be subject to the risk that economic, political or other conditions that have a negative effect on that sector or commodity will negatively impact the Fund to a greater extent than if the Fund’s assets were invested in a wider variety of sectors or commodities.

Subsidiary Risk: By investing in the Subsidiary, the Fund is indirectly exposed to the risks associated with the Subsidiary’s investments. The derivatives and other investments held by the Subsidiary are the same as those that are permitted to be held by the Fund and are subject to the same risks that apply to similar investments if held directly by the Fund. The Subsidiary is not registered under the Investment Company Act of 1940 (the “Investment Company Act”), and, unless otherwise noted in this prospectus, is not subject to all of the investor protections of the Investment Company Act. In addition, changes in the laws of the United States and/or the Cayman Islands could result in the inability of the Fund and/or the Subsidiary to operate as described in this Prospectus and the Statement of Additional Information and could adversely affect the Fund.

U.S. Government Securities Risk: Securities issued or guaranteed by U.S. government agencies or government-sponsored entities may not be backed by the full faith and credit of the U.S. government. As a result, no assurance can be given that the U.S. government

will provide financial support to these securities or issuers (such as securities issued by the Federal National Mortgage Association, or the Federal Home Loan Mortgage Corporation). Although certain government securities are backed by the full faith and credit of the U.S. government (such as securities issued by the Government National Mortgage Association), circumstances could arise that would delay or prevent the payment of interest or principal. It is possible that issuers of U.S. government securities will not have the funds to meet their payment obligations in the future and, in these circumstances, the Fund’s returns may be adversely affected.

Performance

The following bar chart and tables are intended to help you understand the risks and potential rewards of investing in the Fund. The bar chart shows the performance of the Fund for the period shown. The table shows how the Fund’s average annual total returns compare to a broad measure of market performance and an additional index over time. Please note that the Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. To obtain updated performance information please visit the Fund’s website at harborcapital.com or call 800-422-1050.

Calendar Year Total Returns

During the time period shown in the bar chart, the Fund’s highest and lowest returns for a calendar quarter were:

	Total Returns	Quarter/Year
Best Quarter	7.83%	Q4 2023
Worst Quarter	-1.16%	Q4 2024

Summary Prospectus

Harbor Multi-Asset Total Return ETF (formerly, Harbor Multi-Asset Explorer ETF)

Average Annual Total Returns — As of December 31, 2025

	One Year	Annualized	Inception Date
	One Year	Since Inception	Inception Date
Harbor Multi-Asset Total Return ETF
Before Taxes	18.56%	16.41%	09/13/2023
After Taxes on Distributions	17.38%	14.97%
After Taxes on Distributions and Sale of Fund Shares	11.20%	12.19%
Comparative Indices (reflects no deduction for fees, expenses or taxes)
S&P 500 Index^	17.88%	22.03%
ICE BofA 0-3 Month US Treasury Bill Total Return Index^^	4.28%	4.89%

This index represents a broad measure of market performance.

The Advisor considers this index to be the appropriate benchmark index for the Fund for performance comparison purposes.

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns will depend on a shareholder’s individual tax situation and may differ from those shown. The after-tax returns shown are not relevant to tax-exempt shareholders or shareholders who hold their Fund shares through a tax-deferred arrangement, such as a 401(k) plan or individual retirement account. In some cases, average annual total return “After Taxes on Distributions and Sale of Fund Shares” may exceed the return “Before Taxes” and/or “After Taxes on Distributions” due to an assumed tax benefit for any losses on a sale of Fund shares at the end of the measurement period.

Portfolio Management

Investment Advisor

Harbor Capital Advisors, Inc.

Portfolio Managers

The portfolio managers are jointly and primarily responsible for the day-to-day investment decision making for the Fund.

Spenser P. Lerner, CFA, Head of Multi-Asset Solutions, Managing Director and Portfolio Manager of Harbor Capital Advisors, Inc., has managed the Fund since 2023.

Justin Menne, CFA, Head of Global Equities at Harbor Capital Advisors, Inc., has managed the Fund since 2023.

Jonathan G. Poynter, PhD, CFA, Head of Quantitative Research at Harbor Capital Advisors, Inc., has managed the Fund since 2023.

Jake Schurmeier, Portfolio Manager at Harbor Capital Advisors, Inc., has managed the Fund since 2023.

Buying and Selling Fund Shares

Individual Fund shares may only be bought and sold in the secondary market through a broker or dealer at a market price. Shares of the Fund are listed and traded on an exchange at market price throughout the day rather than at NAV and may trade at a price greater than the Fund’s NAV (premium) or less than the Fund’s NAV (discount). An investor may incur costs attributable

to the difference between the highest price a buyer is willing to pay to purchase shares (bid) and the lowest price a seller is willing to accept for shares (ask) when buying or selling Fund shares in the secondary market (the “bid-ask spread”). Recent information, including information regarding the Fund’s NAV, market price, premiums and discounts, and bid-ask spread, is available at harborcapital.com.

Tax Information

Distributions you receive from the Fund are subject to federal income tax and may also be subject to state and local taxes. These distributions will generally be taxed as ordinary incomeor capital gains, unless you are investing through a tax-deferred retirement account, such as a 401(k) plan or individual retirement account. Investments in tax-deferred accounts may be subject to tax when they are withdrawn.

Payments to Broker-Dealers and Other Financial Intermediaries

The Advisor and/or its related companies have in the past and could in the future pay intermediaries, which may include banks, broker-dealers, or financial professionals, for marketing activities and presentations, educational training programs, conferences, the development of technology platforms and reporting systems and data or other services related to the sale of Fund shares and related services. These payments create a conflict of interest by influencing the broker-dealer or other intermediary and your sales representative to recommend the Fund over another investment. Ask your sales representative or visit your financial intermediary’s website for more information.

Exchange	Ticker

NYSE Arca, Inc.	MATR