Form 8-K

8-K — PIMCO CORPORATE & INCOME OPPORTUNITY FUND

Accession: 0001193125-26-280733

Filed: 2026-06-24

Period: 2026-06-23

CIK: 0001190935

Item: Other Events

Item: Financial Statements and Exhibits

Documents

8-K — d120429d8k.htm (Primary)

EX-99.1 (d120429dex991.htm)

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(D)

OF THE SECURITIES EXCHANGE ACT OF 1934

Date of report (Date of earliest event reported) June 23, 2026

PIMCO Corporate & Income Opportunity Fund

(Exact Name of Registrant as Specified in Its Charter)

Massachusetts

811-21238

46-6121513

(State or other jurisdiction

of incorporation)

(Commission File Number)

(IRS Employer

Identification No.)

1633 Broadway

New York, NY

10019

(Address of principal executive offices)

(Zip Code)

(844) 337-4626

(Registrant’s telephone number, including area code)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class

Trading

Symbol(s)

Name of each exchange

on which registered

Common shares

PTY

New York Stock Exchange

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 8.01 Other Events.

On June 23, 2026, the Board of Trustees approved a change to the Fund’s 80% investment policy. Effective August 28, 2026, the Fund invests, under normal circumstances, at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in corporate debt obligations of varying maturities and/or income-producing investments, which may include those of non-corporate issuers. The supplement to the Fund’s prospectus and statement of additional information disclosing this change is attached hereto as Exhibit 99.1.

Item 9.01 Financial Statements and Exhibits.

(d)

Exhibits

99.1

Supplement, dated June 24, 2026

104

Cover Page Interactive Data File (embedded within the Inline XBRL document)

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

PIMCO Corporate & Income Opportunity Fund

By:

/s/ Ryan G. Leshaw

Name:

Ryan G. Leshaw

Title:

Chief Legal Officer and Secretary

Date: June 24, 2026

EX-99.1

Filename: d120429dex991.htm · Sequence: 2

EX-99.1

PIMCO Corporate & Income Opportunity Fund

(the “Fund”)

Important Notice Regarding Change in Investment Policy

Supplement dated June 24, 2026 to the Fund’s Prospectus dated September 28, 2023, as supplemented from time to time (the

“Prospectus”); and to the Statement of Additional Information dated September 28, 2023, as supplemented from time to time (the “SAI”)

On June 23, 2026, the Board of Trustees approved changes to the Fund’s 80% investment policy. Effective

August 28, 2026, the Fund invests, under normal circumstances, at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in corporate debt obligations of varying maturities and/or income-producing investments,

which may include those of non-corporate issuers.

Accordingly, effective

August 28, 2026, the Fund’s Prospectus and SAI are revised as shown below.

Prospectus

The first sentence of the first paragraph under the “Portfolio Contents” section on the cover page of the

Fund’s Prospectus is deleted and replaced with the following:

The Fund invests, under normal circumstances, at least 80% of its

net assets (plus the amount of any borrowings for investment purposes) in corporate debt obligations of varying maturities and/or income-producing investments, which may include those of non-corporate issuers.

Income-producing investments may include income-producing Fixed Income Instrument investments, dividend-paying equity securities, derivatives on either of the foregoing, derivatives providing exposure to other types of income-producing instruments,

and any other instrument or arrangement that is structured to produce income, including any derivatives position that produces income or the sale of which produces a premium payment. “Fixed Income Instruments” include bonds, debt

securities, bank loans and other similar instruments issued by various U.S. and non-U.S. public- or private-sector entities.

The first sentence of the first paragraph under the “Prospectus Summary—Portfolio Contents” section of

the Prospectus and the first sentence of the first paragraph under the “Portfolio Contents” section of the Prospectus are deleted and replaced with the following:

The Fund invests, under normal circumstances, at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in

corporate debt obligations of varying maturities and/or income-producing investments, which may include those of non-corporate issuers (the “80% Policy”).

The last sentence of the third paragraph under the “Investment Objective and Policies” section of the

Prospectus is deleted and replaced with the following:

The Fund may not change its 80% Policy unless it provides shareholders with at

least 60 days’ written notice of such change.

The following is added as the new fourth sentence of the first

paragraph under the “Prospectus Summary—Portfolio Contents” section of the Prospectus and the new fourth sentence of the first paragraph under the “Portfolio Contents” section of the Prospectus:

Income-producing investments may include income-producing Fixed Income Instrument investments, dividend-paying equity securities, derivatives

on either of the foregoing, derivatives providing exposure to other types of income-producing instruments, and any other instrument or arrangement that is structured to produce income, including any derivatives position that produces income or the

sale of which produces a premium payment.

The following is added to the end of the first paragraph under the

“Portfolio Contents—Derivatives” section of the Prospectus:

Derivative instruments used by the Fund are expected to

be counted towards the Fund’s 80% Policy to the extent they provide investment exposure to investments within that Policy or to one or more of the market risk factors associated with investments included in that Policy.

The following is added as a new paragraph under the “Portfolio Contents” section of the Prospectus:

Fixed Income Instruments

“Fixed Income Instruments,” as used generally in this prospectus, includes:

•

securities issued or guaranteed by the U.S. Government, its agencies or government-sponsored enterprises

(“U.S. Government Securities”);

•

corporate debt securities of U.S. and non-U.S. issuers, including

convertible securities and corporate commercial paper;

•

mortgage-backed and other asset-backed securities;

•

inflation-indexed bonds issued both by governments and corporations;

•

structured notes, including hybrid or “indexed” securities and event-linked bonds;

•

bank capital and trust preferred securities;

•

loans, including participations in and assignments thereof;

•

delayed draw and delayed funding loans and revolving credit facilities;

•

bank certificates of deposit, fixed time deposits and bankers’ acceptances;

•

repurchase agreements on Fixed Income Instruments and reverse repurchase agreements on Fixed Income

Instruments;

•

debt securities issued by states or local governments and their agencies, authorities and other

government-sponsored enterprises;

•

obligations of non-U.S. governments or their subdivisions, agencies

and government-sponsored enterprises; and

•

obligations of international agencies or supranational entities.

Securities issued by U.S. Government agencies or government-sponsored enterprises may not be guaranteed by the U.S. Treasury.

The Fund, to the extent permitted by the 1940 Act, the rules thereunder or any exemptive relief therefrom, may invest in derivatives based on

Fixed Income Instruments.

SAI

The ninth paragraph under the “INVESTMENT RESTRICTIONS—Other Information Regarding Investment

Restrictions” section of the Fund’s SAI is deleted and replaced with the following:

The Fund may not change its policy to

invest at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in corporate debt obligations of varying maturities and/or income-producing investments, which may include those of

non-corporate issuers (the “80% Policy”), unless it provides shareholders with at least 60 days’ written notice of such change.

The first sentence of the twelfth paragraph under the “INVESTMENT

RESTRICTIONS—Other Information Regarding Investment Restrictions” section of the Fund’s SAI is deleted and replaced with the following:

Except as otherwise required by applicable regulation, for purposes of its investment policies and restrictions, the Fund may value derivative

instruments at market value, notional value or full exposure value (i.e., the sum of the notional amount for the contract plus the market value), or any combination of the foregoing (e.g., notional value for purposes of calculating the numerator and

market value for purposes of calculating the denominator for compliance with a particular policy or restriction).

The

fourth sentence of the twelfth paragraph under the “INVESTMENT RESTRICTIONS—Other Information Regarding Investment Restrictions” section of the Fund’s SAI is deleted.

Investors Should Retain This Supplement for Future Reference

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