PIMCO Mortgage Opportunities and Bond Fund

Summary Prospectus

August 1, 2026

Share Class:	Inst	I-2	I-3	A	C
Ticker:	PMZIX	PMZPX	PMZNX	PMZAX	PMZCX

Before you invest, you may want to review the Fund’s prospectus, which, as supplemented, contains more information about the Fund and its risks. You can find the Fund’s prospectus, reports to shareholders and other information about the Fund online at http://investments.pimco.com/prospectuses. You can also get this information at no cost by calling 888.87.PIMCO or by sending an email request to piprocess@sscinc.com. The Fund’s prospectus and Statement of Additional Information, both dated August 1, 2026, as supplemented, are incorporated by reference into this Summary Prospectus.

Investment Objective

The Fund seeks maximum long-term return, consistent with prudent investment management.

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. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $100,000 in Class A shares of eligible funds offered by PIMCO Equity Series and PIMCO Funds. More information about these and other discounts is available in the “Classes of Shares” section on page 91 of the Fund’s prospectus, Appendix B to the Fund’s prospectus (Financial Firm-Specific Sales Charge Waivers and Discounts) or from your financial professional.

Shareholder Fees (fees paid directly from your investment):

	Inst Class	I-2	I-3	Class A	Class C
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	None	None	None	3.75%	None
Maximum Deferred Sales Charge (Load) (as a percentage of the lower of the original purchase price or redemption price)	None	None	None	1.00%	1.00%

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

	Inst Class	I-2	I-3	Class A	Class C
Management Fees	0.60%	0.70%	0.80%	0.75%	0.75%
Distribution and/or Service (12b-1) Fees	N/A	N/A	N/A	0.25%	1.00%
Other Expenses(1)	1.54%	1.54%	1.54%	1.54%	1.54%
Total Annual Fund Operating Expenses	2.14%	2.24%	2.34%	2.54%	3.29%
Fee Waiver and/or Expense Reimbursement(2)	N/A	N/A	(0.05%)	N/A	N/A
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement	2.14%	2.24%	2.29%	2.54%	3.29%

“Other Expenses” include interest expense of 1.54%. Interest expense is borne by the Fund separately from the management fees paid to Pacific Investment Management Company LLC (“PIMCO”). Excluding interest expense, Total Annual Fund Operating

Expenses After Fee Waiver and/or Expense Reimbursement are 0.60%, 0.70%, 0.75%, 1.00% and 1.75% for Institutional Class, I-2, I-3, Class A and Class C shares, respectively.

PIMCO has contractually agreed, through July 31, 2027, to reduce its supervisory and administrative fee for the Fund’s I-3 shares by 0.05% of the average daily net assets attributable to I-3 shares of the Fund. This Fee Waiver Agreement renews annually unless terminated by PIMCO upon at least 30 days’ prior notice to the end of the contract term.

Example. The Example is intended to help you compare the cost of investing in Institutional Class, I-2, I-3, Class A or Class C shares of the Fund with the costs of investing in other mutual funds. The Example assumes that you invest $10,000 in the noted class of shares for the time periods indicated, and then hold or redeem all your shares at the end of those periods. 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, based on these assumptions your costs would be:

If you redeem your shares at the end of each period:

	1 Year	3 Years	5 Years	10 Years
Institutional Class	$217	$670	$1,149	$2,472
I-2	$227	$700	$1,200	$2,575
I-3	$232	$726	$1,246	$2,672
Class A	$622	$1,136	$1,675	$3,143
Class C	$432	$1,013	$1,717	$3,415

If you do not redeem your shares:

	1 Year	3 Years	5 Years	10 Years
Class A	$622	$1,136	$1,675	$3,143
Class C	$332	$1,013	$1,717	$3,415

Portfolio Turnover

The Fund pays transaction costs when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in the Annual Fund Operating Expenses or in the Example tables, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 1004% of the average value of its portfolio.

Principal Investment Strategies

The Fund seeks to achieve its investment objective by investing under normal circumstances at least 80% of its assets in a portfolio of mortgage-related assets, including, but not limited to Agency residential and commercial mortgage-backed securities (“MBS”) and private label residential and commercial MBS, and of Fixed Income Instruments, which may be represented by forwards or derivatives such as options, futures contracts or swap agreements.Agency MBS refers to MBS issued by government-sponsored enterprises, such as the Government National Mortgage Association (“GNMA” or “Ginnie Mae”), the Federal National Mortgage Association (“FNMA” or “Fannie Mae”) or the Federal Home Loan Mortgage Corporation (“FHLMC” or “Freddie Mac”). “Fixed Income Instruments” include bonds, debt securities and other similar

PIMCO Funds | Summary Prospectus

PIMCO Mortgage Opportunities and Bond Fund

instruments issued by various U.S. and non-U.S. public- or private-sector entities. The Fund will invest in a broad array of mortgage-related securities in seeking to generate consistent, absolute returns across full market cycles. The average portfolio duration of this Fund normally varies from 0 to 8 years based on PIMCO’s market forecasts. Duration is a measure used to determine the sensitivity of a security’s price to changes in interest rates. The longer a security’s duration, the more sensitive it will be to changes in interest rates.

The Fund may invest up to 50% of its total assets in high yield securities (“junk bonds”), as rated by Moody’s Ratings (“Moody’s”), Standard & Poor’s Ratings Services (“S&P”) or Fitch Ratings, Inc. (“Fitch”), or, if unrated, as determined by PIMCO (except such limitation shall not apply to the Fund’s investments in mortgage-related securities). In the event that ratings services assign different ratings to the same security, PIMCO will use the highest rating as the credit rating for that security. Mortgage-related securities are interests in pools of residential or commercial mortgage loans, including mortgage loans made by savings and loans institutions, mortgage bankers, commercial banks and others.

The Fund may invest, without limitation, in derivative instruments, such as options, futures contracts, options on futures, fixed income swap agreements, credit default swap agreements and other synthetic mortgage-related swap indices, or in mortgage- or asset-backed securities, subject to applicable law and any other restrictions described in the Fund’s prospectus or Statement of Additional Information. The Fund may invest up to 10% of its total assets in any combination of mortgage-related or other asset-backed interest-only (“IO”), principal-only (“PO”), or inverse floating rate debt (“inverse floater”) securities. The Fund may invest up to 10% of its total assets in mortgage- or real estate-related equity instruments, including preferred securities, common stock, convertible securities and other equity-related instruments. The Fund may purchase or sell securities on a when-issued, delayed delivery or forward commitment basis and may engage in short sales. The Fund may, without limitation, seek to obtain market exposure to the securities in which it primarily invests by entering into a series of purchase and sale contracts or by using other investment techniques (such as buy backs or dollar rolls). The “total return” sought by the Fund consists of income earned on the Fund’s investments, plus capital appreciation, if any, which generally arises from decreases in interest rates or improving credit fundamentals for a particular sector or security.

Principal Risks

It is possible to experience losses on an investment in the Fund. The principal risks of investing in the Fund, which could adversely affect its net asset value, yield and total return, are listed below.

Interest Rate Risk: the risk that fixed income securities will fluctuate in value due to changes or the anticipation of changes in interest rates; a Fund with a longer average portfolio duration will be more sensitive to changes in interest rates than a Fund with a shorter average portfolio duration. Factors such as government and central bank policy, inflation, the economy, and the market for bonds can impact interest rates and yields

Call Risk: the risk that an issuer may exercise its right to redeem a fixed income security earlier than expected (a call). Issuers may call outstanding securities prior to their maturity for a number of reasons including declining interest rates, changes in credit spreads and improvements in the issuer’s credit quality. If an issuer calls a security that the Fund has invested in, the Fund may not recoup the full amount of its initial investment or may not realize the full anticipated earnings from the investment and may be forced to reinvest in lower-yielding securities, securities with greater credit risks or securities with other, less favorable features

Credit Risk: the risk that the Fund could experience losses if the issuer or guarantor of a fixed income security, the counterparty to a derivative contract or a repurchase agreement, a borrower of portfolio securities or the issuer or guarantor of collateral, is unable or unwilling, or is perceived (whether by market participants, rating agencies, pricing services or otherwise) as unable or unwilling, to meet its financial obligations

High Yield Risk: the risk that high yield securities and unrated securities of similar credit quality (commonly known as “junk bonds”) are subject to greater levels of market, credit, call and liquidity risks. High yield securities are considered primarily speculative by rating agencies with respect to the issuer’s continuing ability to make principal and interest payments, and their values may be more volatile than higher-rated securities of similar maturity

Market Risk: the risk that the value of securities owned by the Fund may fluctuate, sometimes rapidly or unpredictably, due to a variety of factors affecting securities markets generally or particular industries or sectors

Issuer Risk: the risk that the value of a security may decline for reasons related to the issuer, such as management performance, changes in financial condition or credit rating, financial leverage, reputation or reduced demand for the issuer’s goods or services

Liquidity Risk: the risk that a particular investment may be difficult to purchase or sell and that the Fund may be unable to sell investments 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, credit tightening and may be magnified in changing interest rate environments or other circumstances where investor redemptions from fixed income funds may be higher than normal, causing increased supply in the market due to selling activity. The liquidity of the Fund’s shares may be constrained by the liquidity of the Fund’s portfolio holdings

Derivatives Risk: the risk of investing in derivative instruments (such as forwards, futures, options, swaps and structured securities) and other similar investments, including leverage, liquidity, interest rate, market, counterparty (including credit), operational, legal and management risks, and valuation complexity. Changes in the value of a derivative or other similar investment may not correlate perfectly with, and may be more sensitive to market events than, the underlying asset, rate or

2 Summary Prospectus | PIMCO Funds

Summary Prospectus

index, and the Fund could lose more than the initial amount invested. Derivatives used for hedging or risk management may not operate as intended or may expose the Fund to additional risks. Changes in the value of a derivative or other similar instrument may also create margin delivery or settlement payment obligations for the Fund. The Fund’s use of derivatives or other similar investments may result in losses to the Fund, a reduction in the Fund’s returns and/or increased volatility. Non-centrally-cleared over-the-counter (“OTC”) derivatives or other similar investments are also subject to the risk that a counterparty to the transaction will not fulfill its contractual obligations to the other party, as many of the protections afforded to centrally-cleared derivative transactions might not be available for non-centrally-cleared OTC derivatives or other similar investments. The primary credit risk on derivatives or other similar investments that are exchange-traded or traded through a central clearing counterparty resides with the Fund's clearing broker or the clearinghouse. Changes in regulations relating to a registered fund’s use of derivatives and related instruments could potentially limit or impact the Fund’s ability to invest in derivatives, limit the Fund’s ability to employ certain strategies that use derivatives or other similar investments and/or adversely affect the value of derivatives or other similar investments and the Fund’s performance

Equity Risk: the risk that the value of equity or equity-related securities, such as common stocks and preferred securities, may decline due to general market conditions which are not specifically related to a particular company or to factors affecting a particular industry or industries. Equity or equity-related securities generally have greater price volatility than fixed income securities. In addition, preferred securities may be subject to greater credit risk or other risks, such as risks related to deferred and omitted distributions, limited voting rights, liquidity, interest rates, regulatory changes and special redemption rights

Mortgage-Related and Other Asset-Backed Securities Risk: the risks of investing in mortgage-related and other asset-backed securities, including interest rate risk, extension risk, prepayment risk and credit risk. The Fund may invest in any tranche of mortgage-related and other asset-backed securities, including junior and/or equity tranches (to the extent consistent with the Fund’s guidelines), which generally carry higher levels of the foregoing risks

Collateralized Loan Obligations Risk: the risk that investing in collateralized loan obligations (“CLOs”) and other similarly structured investments exposes the Fund to heightened credit risk, interest rate risk, liquidity risk, market risk and prepayment and extension risk, as well as the risk of default on the underlying asset. In addition, investments in CLOs carry additional risks, including, but not limited to: (i) the possibility that distributions from collateral securities will not be adequate to make interest or other payments; (ii) the quality of the collateral may decline in value or default; (iii) risks related to the capability of the servicer of the securitized assets; (iv) the risk that the Fund may invest in tranches of CLOs that are subordinate to other tranches; (v) the structure and complexity of the transaction and the legal documents may not be fully understood at the time of investment and could lead to disputes with the issuer or among investors regarding

the characterization of proceeds or unexpected investment results; and (vi) the CLO's manager may perform poorly

Extension Risk: the risk that, in periods of rising interest rates, issuers of mortgage-related and other asset-backed securities may pay principal later than expected, which may reduce the value of the Fund’s investment in such securities and may prevent the Fund from receiving higher interest rates on proceeds reinvested

Prepayment Risk: the risk that, in periods of declining interest rates, issuers of mortgage-related and other asset-backed securities may pay principal more quickly than expected, which results in the Fund foregoing future interest income on the portion of the principal repaid early and may result in the Fund being forced to reinvest investment proceeds at lower interest rates

Privately Issued Mortgage-Related Securities Risk: the risk of non-payment because there are no direct or indirect government, agency or government-sponsored entity guarantees of payments in the pools created by non-governmental issuers

Real Estate Risk: the risk that the Fund’s investments in real estate investment trusts (“REITs”) or real estate-linked derivative instruments will subject the Fund to risks similar to those associated with direct ownership of real estate, including risks related to losses from casualty or condemnation, changes in local and general economic conditions, fluctuations in supply and demand, interest rate changes, zoning laws, regulatory limitations on rents, property taxes and operating expenses. The Fund’s investments in REITs or real estate-linked derivative instruments subject it to management and tax risks. In addition, REITs that are privately held or not traded on a national securities exchange may subject the Fund to liquidity and valuation risk

Leveraging Risk: the risk that certain transactions of the Fund, such as reverse repurchase agreements, loans of portfolio securities, and the use of when-issued, delayed delivery or forward commitment transactions, and derivative instruments, may give rise to leverage, magnifying gains and losses and causing the Fund to be more volatile than if it had not been leveraged. This means that leverage entails a heightened risk of loss. The use of leverage may also increase the Fund’s sensitivity to interest rate changes and other market risks

Management Risk: the risk that the investment techniques and risk analyses applied by PIMCO will not produce the desired results and that actual or potential conflicts of interest, legislative, regulatory or tax restrictions, policies or developments may affect the investment techniques available to PIMCO in connection with managing the Fund and may cause PIMCO to restrict or prohibit participation in certain investments. There is no guarantee that the investment objective of the Fund will be achieved

Short Exposure Risk: the risk of entering into short sales or other short positions, including the potential loss of more money than the actual cost of the investment, and the risk that the third party to the short sale or other short position will not fulfill its contractual obligations, causing a loss to the Fund

August 1, 2026 | SUMMARY PROSPECTUS 3

PIMCO Mortgage Opportunities and Bond Fund

Convertible Securities Risk: as convertible securities share both fixed income and equity characteristics, they are subject to risks to which fixed income and equity investments are subject. These risks include equity risk, interest rate risk, market risk, liquidity risk and credit risk

Distribution Rate Risk: the risk that the Fund’s distribution rate may change unexpectedly as a result of numerous factors, including changes in realized and projected market returns, fluctuations in market interest rates, Fund performance and other factors

Turnover Risk: the risk that high levels of portfolio turnover may increase transaction costs and taxes and may lower investment performance

Please see “Description of Principal Risks” in the Fund's prospectus for a more detailed description of the risks of investing in the Fund. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Performance Information

The performance information shows summary performance information for the Fund in a bar chart and an Average Annual Total Returns table. The information provides some indication of the risks of investing in the Fund by showing changes in its performance from year to year and by showing how the Fund’s average annual returns compare with the returns of certain indexes. Absent any applicable fee waivers and/or expense limitations, performance would have been lower. The bar chart shows performance of the Fund’s Institutional Class shares. For periods prior to the inception date of I-3 shares (April 27, 2018), performance information shown in the table for that class is based on the performance of the Fund’s Institutional Class shares, adjusted to reflect the fees and expenses paid by that class of shares. Performance for Class A and Class C shares in the Average Annual Total Returns table reflects the impact of sales charges. The Fund’s past performance, before and after taxes, is not necessarily an indication of how the Fund will perform in the future.

In addition to the Fund’s performance, the Average Annual Total Returns table includes performance of: (i) a broad-based securities market index (i.e., a regulatory index) and (ii) a supplemental index. It is not possible to invest directly in an unmanaged index. The Fund’s regulatory index is the Bloomberg U.S. Aggregate Index. The Fund’s regulatory index is shown in connection with certain regulatory requirements to provide a broad measure of market performance. The Bloomberg U.S. Aggregate Index represents securities that are SEC-registered, taxable, and dollar denominated. The index covers the U.S. investment grade fixed rate bond market, with index components for government and corporate securities, mortgage pass-through securities, and asset-backed securities. These major sectors are subdivided into more specific indices that are calculated and reported on a regular basis. The supplemental index shown is the ICE BofA SOFR Overnight Rate Index. The ICE BofA SOFR Overnight Rate Index tracks the performance of a synthetic asset paying SOFR to a stated maturity. The index is based on the assumed purchase at par of a synthetic instrument having exactly its stated

maturity and with a coupon equal to that day’s fixing rate. That issue is assumed to be sold the following business day (priced at a yield equal to the current day fixing rate) and rolled into a new instrument. SOFR (Secured Overnight Funding Rate) is an overnight rate (published in arrears) and was chosen by the Alternative Reference Rates Committee (“ARRC”) as the successor to the USD LIBOR (London Interbank Offered Rate). SOFR is secured (collateralized by Treasuries), calculated by the Federal Reserve Bank of New York, and transactions based.

Performance for the Fund is updated daily and quarterly and may be obtained as follows: daily and quarterly updates on the net asset value and performance page at https://www.pimco.com/us/en/product-finder.

Calendar Year Total Returns — Institutional Class

Best Quarter	June 30, 2020	4.92%
Worst Quarter	June 30, 2022	-4.17%
Year-to-Date	June 30, 2026	1.15%

Average Annual Total Returns (for periods ended 12/31/25)

	1 Year	5 Years	10 Years
Institutional Class Return Before Taxes(1)	8.52%	3.12%	3.80%
Institutional Class Return After Taxes on Distributions(1)	5.93%	0.58%	1.60%
Institutional Class Return After Taxes on Distributions and Sales of Fund Shares(1)	4.99%	1.25%	1.92%
I-2 Return Before Taxes	8.42%	3.02%	3.69%
I-3 Return Before Taxes	8.36%	2.97%	3.64%
Class A Return Before Taxes	4.04%	1.93%	2.99%
Class C Return Before Taxes	6.29%	1.94%	2.61%
Bloomberg U.S. Aggregate Index (reflects no deductions for fees, expenses or taxes)	7.30%	-0.36%	2.01%
ICE BofA SOFR Overnight Rate Index (reflects no deductions for fees, expenses or taxes)(2)	4.39%	3.31%	-

After-tax returns are calculated using the highest historical individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. In some cases the return after taxes may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period. After-tax returns are for Institutional Class shares only. After-tax returns for other classes will vary.

ICE BofA SOFR Overnight Rate Index was first published on October 1, 2019.

4 Summary Prospectus | PIMCO Funds

Summary Prospectus

Investment Adviser/Portfolio Managers

PIMCO serves as the investment adviser for the Fund. The Fund‘s portfolio is jointly and primarily managed by Joshua Anderson, Daniel Hyman, Alfred Murata, Jing Yang and Munish Gupta. Messrs. Anderson, Hyman and Murata are Managing Directors of PIMCO. They have managed the Fund since its inception in October 2012. Ms. Yang is a Managing Director of PIMCO and has managed the Fund since July 2018. Mr. Gupta is an Executive Vice President of PIMCO and has managed the Fund since August 2022.

Purchase and Sale of Fund Shares

Fund shares may be purchased or sold (redeemed) on any business day (normally any day when the New York Stock Exchange (“NYSE”) is open). Generally, purchase and redemption orders for Fund shares are processed at the net asset value next calculated after an order is received by the Fund.

Institutional Class, I-2 and I-3

The minimum initial investment for Institutional Class, I-2 and I-3 shares of the Fund is $1 million, except that the minimum initial investment may be modified for certain financial firms that submit orders on behalf of their customers.

You may sell (redeem) all or part of your Institutional Class, I-2 and I-3 shares of the Fund on any business day. If you are the registered owner of the shares on the books of the Fund, depending on the elections made on the Account Application, you may sell by:

■

Sending a written request by regular mail to:

PIMCO Funds
P.O. Box 219024, Kansas City, MO 64121-9024
or by overnight mail to:
PIMCO Funds c/o SS&C Global Investor and Distribution Solutions, Inc.

801 Pennsylvania Avenue, STE 219024, Kansas City, MO 64105-1307

■

Calling us at 888.87.PIMCO and a Shareholder Services associate will assist you

■

Sending a fax to our Shareholder Services department at 816.421.2861

■

Sending an e-mail to piprocess@sscinc.com

Class A and Class C

The minimum initial investment for Class A and Class C shares of the Fund is $1,000. The minimum subsequent investment for Class A and Class C shares is $50. The minimum initial investment may be modified

for certain financial firms that submit orders on behalf of their customers. You may purchase or sell (redeem) all or part of your Class A and Class C shares through a broker-dealer, or other financial firm, or, if you are the registered owner of the shares on the books of the Fund, by regular mail to PIMCO Funds, P.O. Box 219294, Kansas City, MO 64121-9294 or overnight mail to PIMCO Funds, c/o SS&C Global Investor and Distribution Solutions, Inc., 801 Pennsylvania Avenue, STE 219294, Kansas City, MO 64105-1307. The Fund reserves the right to require payment by wire or U.S. Bank check in connection with accounts opened directly with the Fund by Account Application.

Tax Information

The Fund’s distributions are generally taxable to you as ordinary income, capital gains, or a combination of the two, unless you are investing through a tax-deferred arrangement, such as a 401(k) plan or an individual retirement account, in which case distributions may be taxable upon withdrawal.

Payments to Broker-Dealers and Other Financial Firms

If you purchase shares of the Fund through a broker-dealer or other financial firm (such as a bank), the Fund and/or its related companies (including PIMCO) may pay the financial firm for the sale of those shares of the Fund and/or related services. These payments may create a conflict of interest by influencing the broker-dealer or other financial firm and your salesperson to recommend the Fund over another investment. Ask your salesperson or visit your financial firm’s website for more information.

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