PIMCO Short Asset Investment Fund

SUMMARY PROSPECTUS

July 30, 2018 (as supplemented December 7, 2018)

Share Class:	Inst	I-2	I-3	M	Admin	A
Ticker:	PAIDX	PAIPX	PANDX	PAMSX	PAIQX	PAIAX

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 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@dstsystems.com. The Fund's prospectus and Statement of Additional Information, both dated July 30, 2018, as supplemented, along with the financial statements included in the Fund's most recent annual report to shareholders dated March 31, 2018, are incorporated by reference into this Summary Prospectus.

Investment Objective

The Fund seeks maximum current income, consistent with daily liquidity.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. In addition to the fees and expenses described below, you may also be required to pay brokerage commissions on purchases and sales of Institutional Class, I-2 or I-3 shares of the Fund. 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 34 of the Fund's prospectus, Appendix B to the Fund's prospectus (Financial Firm-Specific Sales Charge Waivers and Discounts) or from your financial advisor.

Shareholder Fees (fees paid directly from your investment):

	Inst Class	I-2	I-3	Class M	Admin Class	Class A
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	None	None	None	None	None	2.25%
Maximum Deferred Sales Charge (Load) (as a percentage of the lower of the original purchase price or redemption price)	None	None	None	None	None	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 M	Admin Class	Class A
Management Fees	0.34%	0.44%	0.54%	0.34%	0.34%	0.44%
Distribution and/or Service (12b-1) Fees	N/A	N/A	N/A	N/A	0.25%	0.25%
Other Expenses(1)	0.03%	0.03%	0.03%	0.03%	0.03%	0.03%
Total Annual Fund Operating Expenses	0.37%	0.47%	0.57%	0.37%	0.62%	0.72%
Fee Waiver and/or Expense Reimbursement(2)(3)	(0.03%)	(0.03%)	(0.08%)	(0.03%)	(0.03%)	(0.03%)
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement	0.34%	0.44%	0.49%	0.34%	0.59%	0.69%

1"Other Expenses" include interest expense of 0.03%. 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 0.31%, 0.41%, 0.46%, 0.31%, 0.56% and 0.66% for Institutional Class, I-2, I-3, Class M, Administrative Class and Class A shares, respectively.

2PIMCO has contractually agreed, through July 31, 2019, to reduce its advisory fee by 0.03% of the average daily net assets 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. Under certain conditions, PIMCO may recoup amounts reduced in future periods, not exceeding three years.

3PIMCO has contractually agreed, through July 31, 2019, 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 M, Administrative Class or Class A 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 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. Investors may pay brokerage commissions on their purchases and sales of Institutional Class, I-2 or I-3 shares of the Fund, which are not reflected in the Example. 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	$35	$116	$205	$465
I-2	$45	$148	$260	$589
I-3	$50	$175	$310	$706
Class M	$35	$116	$205	$465
Administrative Class	$60	$195	$343	$771
Class A	$294	$447	$614	$1,097

If you do not redeem your shares:

	1 Year	3 Years	5 Years	10 Years
Class A	$294	$447	$614	$1,097

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 123% 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 65% of its total assets in a diversified

PIMCO FUNDS | SUMMARY PROSPECTUS

PIMCO Short Asset Investment Fund

portfolio of Fixed Income Instruments of varying maturities, which may be represented by forwards or derivatives such as options, futures contracts or swap agreements. "Fixed Income Instruments" include bonds, debt securities and other similar instruments issued by various U.S. and non-U.S. public- or private-sector entities. The average portfolio duration of this Fund will vary based on Pacific Investment Management Company LLC's ("PIMCO") market forecasts and will normally not exceed one and one-half years. 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 invests primarily in investment grade debt securities rated Baa or higher by Moody's Investors Service, Inc. ("Moody's"), or equivalently rated by Standard & Poor's Ratings Services ("S&P") or Fitch, Inc. ("Fitch"), or, if unrated, determined by PIMCO to be of comparable quality. The Fund may not invest in securities denominated in foreign currencies, but may invest without limit in U.S. dollar-denominated securities of foreign issuers. In addition, the Fund may invest up to 10% of its total assets in U.S. dollar-denominated securities and instruments that are economically tied to emerging market countries. The Fund may invest up to 60% of its total assets in corporate issuers. 

The Fund may invest, without limitation, in derivative instruments, such as options, futures contracts or swap agreements, 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 20% of its total assets in asset-backed securities and up to 10% of its total assets in privately issued mortgage-backed securities. The Fund may invest up to 10% of its total assets in interest rate swaps and up to 5% of its total assets in credit default swaps. 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).  

Principal Risks

It is possible to lose money 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 decline in value because of an increase 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

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 (e.g., 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 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 lose money if the issuer or guarantor of a fixed income security, or the counterparty to a derivative contract, is unable or unwilling to meet its financial obligations

Market Risk: the risk that the value of securities owned by the Fund may go up or down, sometimes rapidly or unpredictably, due to factors affecting securities markets generally or particular industries

Issuer Risk: the risk that the value of a security may decline for a reason directly related to the issuer, such as management performance, financial leverage and 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 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

Derivatives Risk: the risk of investing in derivative instruments (such as futures, swaps and structured securities), including leverage, liquidity, interest rate, market, credit and management risks, mispricing or valuation complexity. Changes in the value of the derivative may not correlate perfectly with, and may be more sensitive to market events than, the underlying asset, rate or index, and the Fund could lose more than the initial amount invested. The Fund's use of derivatives may result in losses to the Fund, a reduction in the Fund's returns and/or increased volatility. Over-the-counter ("OTC") derivatives 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 OTC derivatives. For derivatives traded on an exchange or through a central counterparty, credit risk resides with the Fund's clearing broker, or the clearinghouse itself, rather than with a counterparty in an OTC derivative transaction. Changes in regulation relating to a mutual 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 and/or adversely affect the value of derivatives and the Fund's performance

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

Foreign (Non-U.S.) Investment Risk: the risk that investing in foreign (non-U.S.) securities may result in the Fund experiencing more rapid and extreme changes in value than a fund that invests exclusively in securities of U.S. companies, due to smaller markets, differing reporting, accounting and auditing standards, increased risk of delayed settlement of portfolio transactions or loss of certificates of portfolio securities, and the risk of unfavorable foreign government actions, including nationalization, expropriation or confiscatory taxation, currency blockage, or political changes or diplomatic developments. Foreign securities may also be less liquid and more difficult to value than securities of U.S. issuers

2      SUMMARY PROSPECTUS | PIMCO FUNDS     

Summary Prospectus

Emerging Markets Risk: the risk of investing in emerging market securities, primarily increased foreign (non-U.S.) investment 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, or 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

Management Risk: the risk that the investment techniques and risk analyses applied by PIMCO will not produce the desired results and that legislative, regulatory, or tax restrictions, policies or developments may affect the investment techniques available to PIMCO and the individual portfolio manager in connection with managing the Fund. There is no guarantee that the investment objective of the Fund will be achieved

Short Exposure Risk: the risk of entering into short sales, 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 will not fulfill its contractual obligations, causing a loss to the Fund

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 a broad-based securities market index and an index of similar funds. 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 Class M shares (December 21, 2015), 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 Class M shares. Performance for Class A shares in the Average Annual Total Returns table reflects the impact of sales charges. To obtain the Fund's current yield, call 888.87.PIMCO. Because I-3 shares of the Fund had not commenced operations as of December 31, 2017, no performance for I-3 shares is provided. The Fund's past performance, before and after taxes, is not necessarily an indication of how the Fund will perform in the future.

The Fund's benchmark index is the FTSE 3-Month Treasury Bill Index. The index is an unmanaged index representing monthly return equivalents of yield averages of the last 3-month Treasury Bill issues. The Lipper Ultra-Short Obligation Funds Average is a total return performance average of funds tracked by Lipper, Inc. that invest at least 65% of their assets in investment-grade debt issues or better, and maintain a portfolio dollar-weighted average maturity between 91 and 365 days. It does not reflect deductions for fees, expenses or taxes.

Performance for the Fund is updated daily and quarterly and may be obtained as follows: daily updates on the net asset value and performance page at http://investments.pimco.com/DailyPerformance and quarterly updates at http://investments.pimco.com/QuarterlyPerformance.

Calendar Year Total Returns — Institutional Class*

*The year-to-date return as of June 30, 2018 is 1.02%. For the periods shown in the bar chart, the highest quarterly return was 0.57% in the Q4 2016, and the lowest quarterly return was -0.12% in the Q4 2014.

Average Annual Total Returns (for periods ended 12/31/17)

	1 Year		5 Years		Since Inception (05/31/2012)
Institutional Class Return Before Taxes	1.92	%	1.13	%	1.29	%
Institutional Class Return After Taxes on Distributions(1)	1.09	%	0.62	%	0.78	%
Institutional Class Return After Taxes on Distributions and Sales of Fund Shares(1)	1.10	%	0.63	%	0.76	%
I-2 Return Before Taxes	1.82	%	1.03	%	1.19	%
Class M Return Before Taxes	1.92	%	1.13	%	1.29	%
Administrative Class Return Before Taxes	1.65	%	0.87	%	1.04	%
Class A Return Before Taxes	0.71	%	0.32	%	0.53	%
FTSE 3-Month Treasury Bill Index (reflects no deductions for fees, expenses or taxes)	0.84	%	0.24	%	0.23	%
Lipper Ultra-Short Obligation Funds Average  (reflects no deductions for taxes)	1.40	%	0.70	%	0.78	%

1After-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.

Investment Adviser/Portfolio Manager

PIMCO serves as the investment adviser for the Fund. The Fund's portfolio is managed by Jerome Schneider. Mr. Schneider is a Managing Director of PIMCO, and he has managed the Fund since its inception in May 2012.

July 30, 2018 (as supplemented December 7, 2018) | SUMMARY PROSPECTUS 3

PIMCO Short Asset Investment Fund

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 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, I-3 and Administrative Class

The minimum initial investment for Institutional Class, I-2, I-3 and Administrative Class 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, I-3 and Administrative Class 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 DST Asset Manager Solutions, Inc.
430 W. 7th Street, STE 219024, Kansas City, MO 64105-1407

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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

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Sending an e-mail to piprocess@dstsystems.com

Class A

The minimum initial investment for Class A shares of the Fund is $1,000. The minimum subsequent investment for Class A 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 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 DST Asset Manager Solutions, Inc., 430 W. 7th Street, STE 219294, Kansas City, MO 64105-1407. 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 Web site for more information.

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