Harbor Core Bond Fund

Retirement Class HCBRX

Institutional Class HACBX

Summary Prospectus – March 1, 2025

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, 2025, 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 total return.

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)

	Retirement Class	Institutional Class
Management Fees	0.23%	0.23%
Distribution and Service (12b-1) Fees	None	None
Other Expenses	0.06%	0.14%
Total Annual Fund Operating Expenses	0.29%	0.37%
Expense Reimbursement1	(0.03)%	(0.03)%
Total Annual Fund Operating Expenses After Expense Reimbursement1	0.26%	0.34%

1 The Advisor has contractually agreed to limit the Fund’s operating expenses, excluding interest expense (if any), to 0.26% and 0.34% for the Retirement Class and Institutional Class, respectively, through February 28, 2026. Only the Fund’s Board of Trustees may modify or terminate this agreement.

Expense Example

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated. The 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
Retirement	$27	$90	$160	$365
Institutional	$35	$116	$205	$465

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 101%.

Principal Investment Strategy

The Fund invests primarily in investment-grade fixed income securities of issuers located in the U.S. Under normal market conditions, the Fund invests at least 80% of its net assets, plus borrowings for investment purposes, in a diversified portfolio of fixed income instruments. Fixed income instruments include bonds, debt securities and other similar instruments issued by various public- or private-sector entities.

The Subadvisor’s approach is grounded in detailed bottom-up research and emphasizes careful security selection through:

■

Rigorous fundamental credit analysis of the issuer,

■

A detailed review of the structural features of the security, and

■

Relative-value comparisons to other opportunities.

In order to be selected for the portfolio, a security must be attractive with respect to all three of these factors. If one factor deteriorates, the security becomes a candidate for sale.

When forming an opinion on the creditworthiness of an issuer, the Subadvisor evaluates many factors, including financial performance, balance sheet strength, management quality, operating risk, market position, industry fundamentals, event risk, and economic sensitivity. The Subadvisor’s analysis also includes a detailed review of the underlying structural features of a bond, such as coupon type, redemption features, level of subordination, and collateral. For securitized bonds (such as mortgage-backed and asset-backed), the Subadvisor assesses factors such as issue sponsorship, structure, deal history, regulation, and liquidity. The Subadvisor also evaluates issuers with respect to environmental, social and governance (“ESG”) factors and integrates consideration of these factors into its investment process. The key ESG considerations may vary depending on the industry, sector, geographic region or other factors and the core business of each issuer. The ESG criteria utilized by the Subadvisor is only one factor among others considered in the investment process.

The Subadvisor believes that it is difficult to predict the timing, direction, and magnitude of future interest-rate changes. Therefore, duration management and yield-curve positioning are not part of the Fund’s strategy.

The portfolio is constructed from the bottom up and is comprised of U.S. dollar-denominated securities. The Subadvisor sets sector allocations based on its views of relative values between sectors and opportunities at the security level. A comprehensive risk overlay also influences portfolio construction. The Subadvisor systematically measures and monitors the Fund’s key risk exposures. The overall aim of the portfolio construction process is to craft a portfolio of attractively priced securities (relative to other opportunities in the universe) that when combined together in a portfolio provide what the Subadvisor believes will be attractive expected return, reasonable risk exposures, and adequate liquidity.

At times, the Fund may invest a large percentage of its assets in investment-grade mortgage-backed and asset-backed securities.

Summary Prospectus

Harbor Core Bond Fund

Credit Quality: The Fund invests primarily in investment-grade securities.

Duration: The Fund’s average duration, as calculated by the Subadvisor, is normally equal to that of its benchmark, plus or minus 10%. The duration of the Bloomberg U.S. Aggregate Bond Index as of December 31, 2024 was 6.08 years. Average duration is a weighted average of all bond durations in the Fund’s portfolio, and is an approximate measure of the sensitivity of the market value of the Fund’s holdings to changes in interest rates. If the Fund’s duration is longer than the market’s duration, the Fund would be expected to experience a greater change in the value of its assets when interest rates are rising or falling than would the market as a whole.

Principal Risks

There is no guarantee that the investment objective of the Fund will be achieved. Fixed income securities fluctuate in price in response to various factors, including changes in interest rates, changes in market conditions and issuer-specific events, 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 possible investments. Principal risks impacting the Fund (in alphabetical order after the first four risks) include:

Interest Rate Risk: As interest rates rise, the values of fixed income securities held by the Fund are likely to decrease and reduce the value of the Fund’s portfolio. Securities with longer durations tend to be more sensitive to changes in interest rates and are usually more volatile than securities with shorter durations. For example, a 5 year average duration generally means the price of a fixed income security will decrease in value by 5% if interest rates rise by 1%. Rising interest rates may lead to increased redemptions, increased volatility and decreased liquidity in the fixed income markets, making it more difficult for the Fund to sell its fixed income securities when the Subadvisor may wish to sell or must sell to meet redemptions. During periods when interest rates are low or there are negative interest rates, the Fund’s yield (and total return) also may be low or the Fund may be unable to maintain positive returns or minimize the volatility of the Fund’s net asset value per share. Changing interest rates may have unpredictable effects on the markets, may result in heightened market volatility and may detract from Fund performance. In addition, changes in monetary policy may exacerbate the risks associated with changing interest rates.

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 contractual instrument owned by the Fund could default on its obligation.

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, acts of terrorism, social unrest, natural disasters, recessions, inflation, rapid interest rate changes, supply chain disruptions, sanctions, the spread of infectious illness or other public health threats could also significantly impact the Fund and its investments.

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.

ESG Factors Risk: The consideration of ESG factors by the Subadvisor and/or Advisor, as applicable, could cause the Fund to perform differently than other funds. ESG factors are not the only consideration used by the Subadvisor and/or Advisor, as applicable, in making investment decisions for the Fund and the Fund may invest in a company that scores poorly on ESG factors if it scores well on other criteria. ESG factors may not be considered for every investment decision.

Extension Risk: When interest rates are rising, certain callable fixed income securities may be extended because of slower than expected principal payments. This would lock in a below-market interest rate, increase the security’s duration and reduce the value of the security.

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.

Liquidity Risk: A particular investment may be difficult to purchase or sell and the Fund may be unable to sell illiquid securities at an advantageous time or price or achieve its desired level of exposure to a certain sector. Liquidity risk may result from the lack of an active market, reduced number and capacity of traditional market participants to make a market in fixed income securities, and may be magnified in a rising interest rate environment or other circumstances where investor redemptions from fixed income mutual funds may be higher than normal, causing increased supply in the market due to selling activity. Valuation of investments may be difficult, particularly during periods of market volatility or reduced liquidity and for investments that trade infrequently or irregularly. In these circumstances, among others, an investment may be valued using fair value methodologies that are inherently subjective and reflect good faith judgments based on available information.

Prepayment Risk: When interest rates are declining, the issuer of a fixed income security, including a pass-through security such as a mortgage-backed or an asset-backed security, may exercise its option to prepay principal earlier than scheduled, forcing the Fund to reinvest in lower yielding securities.

Selection Risk: The Subadvisor’s judgment about the attractiveness, value and growth potential of a particular security may be incorrect, which may cause the Fund to underperform. Additionally, the Subadvisor and/or Advisor, as applicable, 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. Thus, investments that a Subadvisor and/or Advisor, as applicable, believes represent an attractive opportunity or in which the Fund seeks to obtain exposure may be unavailable entirely or in the specific quantities or prices sought by a Subadvisor and/or Advisor, as applicable, and the Fund may need to obtain the exposure through less advantageous or indirect investments or forgo the investment at the time.

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

Summary Prospectus

Harbor Core Bond Fund

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 how the performance of the Fund’s Institutional Class has varied from one calendar year to another over the periods shown. The table shows how the Fund’s average annual total returns of the share classes presented compared to the returns of the Fund’s benchmark index, which includes securities with investment characteristics similar to those held by the Fund. 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 for Institutional Class Shares

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

	Total Returns	Quarter/Year
Best Quarter	6.53%	Q4 2023
Worst Quarter	-5.96%	Q1 2022

Average Annual Total Returns — As of December 31, 2024

	One Year	Annualized			Inception Date
	One Year	Five Years	Ten Years	Since Inception	Inception Date
Harbor Core Bond Fund
Retirement Class Before Taxes	1.64%	0.02%	N/A	1.51%	06-01-2018
Institutional Class Before Taxes	1.56%	-0.04%	N/A	1.44%	06-01-2018
After Taxes on Distributions	-0.14%	-1.41%	N/A	0.06%
After Taxes on Distributions and Sale of Fund Shares	0.92%	-0.56%	N/A	0.56%
Comparative Index (reflects no deduction for fees, expenses or taxes)
Bloomberg U.S. Aggregate Bond Index^	1.25%	-0.33%	N/A	1.32%

Since Inception return based on the inception date of the Institutional Class shares.

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. After-tax returns are shown for Institutional Class shares only. After-tax returns for the Retirement Class of shares will vary.

Portfolio Management

Investment Advisor

Harbor Capital Advisors, Inc.

Subadvisor

Income Research + Management (“IR+M”) has subadvised the Fund since 2018.

Summary Prospectus

Harbor Core Bond Fund

Portfolio Managers

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

William A. O’Malley, CFA

Income Research + Management

Mr. O’Malley is a Managing Principal, Senior Portfolio Manager, and Director of Investment Team at IR+M and has served as a portfolio manager for the Fund since 2018.

James E. Gubitosi, CFA

Income Research + Management

Mr. Gubitosi is a Co-Chief Investment Officer at IR+M and has served as a portfolio manager for the Fund since 2018.

Bill O’Neill, CFA

Income Research + Management

Mr. O’Neill is a Senior Portfolio Manager at IR+M and has served as a portfolio manager for the Fund since 2018.

Jake Remley, CFA

Income Research + Management

Mr. Remley is a Senior Portfolio Manager at IR+M and has served as a portfolio manager for the Fund since 2018.

Matt Walker, CFA

Income Research + Management

Mr. Walker is a Senior Portfolio Manager at IR+M and has served as a portfolio manager for the Fund since 2018.

Rachel Campbell, CFA

Income Research + Management

Ms. Campbell is a Portfolio Manager and the Director of Securitized Research at IR+M and has served as a portfolio manager for the Fund since 2018.

Buying and Selling Fund Shares

Shareholders may purchase or sell (redeem) Fund shares on any business day (normally any day the New York Stock Exchange is open). You may conduct transactions by mail, by telephone or through our website.

By Mail	Harbor Funds P.O. Box 804660 Chicago, IL 60680-4108
By Telephone	800-422-1050
By Visiting Our Website	harborcapital.com

Investors who wish to purchase, exchange or redeem shares held through a financial intermediary should contact the financial intermediary directly.

The minimum initial investment amounts are shown below. The minimums may be reduced or waived in some cases. There are no minimums for subsequent investments.

Type of Account	Retirement Class1	Institutional Class
Regular	$1,000,000	$1,000
Individual Retirement Account (IRA)	$1,000,000	$1,000
Custodial (UGMA/UTMA)	$1,000,000	$1,000

1 There is no minimum investment for (1) employer-sponsored group retirement or benefit plans (with more than one participant) that maintain accounts with Harbor Funds at an omnibus or plan level, including: (i) plans established under Internal Revenue Code Sections 401(a), 403(b) or 457, (ii) profit-sharing plans, cash balance plans and money purchase pension plans, (iii) non-qualified deferred compensation plans, and (iv) retiree health benefit plans; and (2) certain wrap or model-driven asset allocation program accounts for the benefit of clients of financial intermediaries, as approved by the Distributor.

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 income or 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 Fund, 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.

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Summary Prospectus

HARBOR CORE BOND FUND

March 1, 2025

Retirement Class	Institutional Class

HCBRX	HACBX

HF.SP.CB.0325

111 South Wacker Drive, 34th Floor

Chicago, IL 60606-4302