BLACKROCK LONG-HORIZON EQUITY FUND

(the “Fund”)

Supplement dated December 28, 2021 to

the Statement of Additional Information of the Fund,

dated August 27, 2021, as supplemented to date

On February 10, 2021, the Board of Trustees (the “Board”) of the Fund approved certain changes to the Fund. Among other things, the Board approved a change in the name of the Fund to “BlackRock Unconstrained Equity Fund” and certain changes to the Fund’s investment objective, investment strategy and investment process. The Board also approved certain changes to the Fund’s fundamental investment restrictions and the Fund’s classification from diversified to non-diversified as defined in the Investment Company Act of 1940, as amended, which required shareholder approval. At a special meeting held on December 23, 2021, shareholders of the Fund approved the changes to the Fund’s fundamental investment restrictions and a change in the Fund’s classification from diversified to non-diversified. The changes to the Fund’s fundamental investment restrictions and the change in the Fund’s classification to non-diversified will take effect on or about February 28, 2022.

Accordingly, effective on or about February 28, 2022, the section of the Statement of Additional Information entitled “Investment Restrictions” is deleted in its entirety and replaced with the following:

II. Investment Restrictions

The Fund has adopted restrictions and policies relating to the investment of the Fund’s assets and its activities. Certain of the restrictions are fundamental policies of the Fund and may not be changed without the approval of the holders of a majority of the Fund’s outstanding voting securities (which for this purpose and under the Investment Company Act, means the lesser of (i) 67% of the shares represented at a meeting at which more than 50% of the outstanding shares are represented or (ii) more than 50% of the outstanding shares). The Fund has also adopted certain non-fundamental investment restrictions, which may be changed by the Board of Trustees without shareholder approval. Set forth below are the Fund’s fundamental and non-fundamental investment restrictions. Unless otherwise provided, all references below to the assets of the Fund are in terms of current market value.

Under its fundamental investment restrictions, the Fund may not:

1. Concentrate its investments in a particular industry, as that term is used in the Investment Company Act.

2. Borrow money, except as permitted under the Investment Company Act.

3. Issue senior securities to the extent such issuance would violate the Investment Company Act.

4. Purchase or hold real estate, except the Fund may purchase and hold securities or other instruments that are secured by, or linked to, real estate or interests therein, securities of real estate investment trusts, mortgage-related securities and securities of issuers engaged in the real estate business, and the Fund may purchase and hold real estate as a result of the ownership of securities or other instruments.

5. Underwrite securities issued by others, except to the extent that the sale of portfolio securities by the Fund may be deemed to be an underwriting or as otherwise permitted by applicable law.

6. Purchase or sell commodities or commodity contracts, except as permitted by the Investment Company Act.

7. Make loans to the extent prohibited by the Investment Company Act.

Notations Regarding the Fund’s Fundamental Investment Restrictions

The following notations are not considered to be part of the Fund’s fundamental investment restrictions and are subject to change without shareholder approval.

With respect to the fundamental policy relating to concentration set forth in (1) above, the Investment Company Act does not define what constitutes “concentration” in an industry. The Commission staff has taken the position that investment of 25% or more of a fund’s total assets in one or more issuers conducting their principal activities in the same industry or group of industries constitutes concentration. It is possible that interpretations of concentration could change in the future. The policy in (1) above will be interpreted to refer to concentration as that term may be interpreted from time to time. The policy also will be interpreted to permit investment without limit in the following: securities of the U.S. government and its agencies or instrumentalities; securities of state, territory, possession or municipal governments and their authorities, agencies, instrumentalities or political subdivisions; and repurchase agreements collateralized by any such obligations. Accordingly, issuers of the foregoing securities will not be considered to be members of any industry. There also will be no limit on investment in issuers domiciled in a single jurisdiction or country. Finance companies will be considered to be in the industries of their parents if their activities are primarily related to financing the activities of the parents. Each foreign government will be considered to be a member of a separate industry. With respect to the Fund’s industry classifications, the Fund currently utilizes any one or more of the industry sub-classifications used by one or more widely recognized market indexes or rating group indexes, and/or as defined by Fund management. The policy also will be interpreted to give broad authority to the Fund as to how to classify issuers within or among industries.

With respect to the fundamental policy relating to borrowing money set forth in (2) above, the Investment Company Act permits the Fund to borrow money in amounts of up to one-third of the Fund’s total assets from banks for any purpose, and to borrow up to 5% of the Fund’s total assets from banks or other lenders for temporary purposes. (The Fund’s total assets include the amounts being borrowed.) In addition, the Fund has received an exemptive order from the SEC permitting it to borrow through the Interfund Lending Program (discussed below), subject to the conditions of the exemptive order. To limit the risks attendant to borrowing, the Investment Company Act requires the Fund to maintain at all times an “asset coverage” of at least 300% of the amount of its borrowings. Asset coverage means the ratio that the value of the Fund’s total assets (including amounts borrowed), minus liabilities other than borrowings, bears to the aggregate amount of all borrowings. Borrowing money to increase portfolio holdings is known as “leveraging.” Certain trading practices and investments, such as reverse repurchase agreements, may be considered to be borrowings or involve leverage and thus are subject to the Investment Company Act restrictions. In accordance with Commission staff guidance and interpretations, when the Fund engages in such transactions, the Fund instead of maintaining asset coverage of at least 300%, may segregate or earmark liquid assets, or enter into an offsetting position, in an amount at least equal to the Fund’s exposure, on a mark-to-market basis, to the transaction (as calculated pursuant to requirements of the Commission). The policy in (2) above will be interpreted to permit the Fund to engage in trading practices and investments that may be considered to be borrowing or to involve leverage to the extent permitted by the Investment Company Act and to permit the Fund to segregate or earmark liquid assets or enter into offsetting positions in accordance with the Investment Company Act. Short-term credits necessary for the settlement of securities transactions and arrangements with respect to securities lending will not be considered to be borrowings under the policy. Practices and investments that may involve leverage but are not considered to be borrowings are not subject to the policy.

With respect to the fundamental policy relating to underwriting set forth in (5) above, the Investment Company Act does not prohibit the Fund from engaging in the underwriting business or from underwriting the securities of other issuers; in fact, in the case of diversified funds, the Investment Company Act permits the Fund to have underwriting commitments of up to 25% of its assets under certain circumstances. Those circumstances currently are that the amount of the Fund’s underwriting commitments, when added to the value of the Fund’s investments in issuers where the Fund owns more than 10% of the outstanding voting securities of those issuers, cannot

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exceed the 25% cap. A fund engaging in transactions involving the acquisition or disposition of portfolio securities may be considered to be an underwriter under the Securities Act of 1933, as amended (the “Securities Act”). Although it is not believed that the application of the Securities Act provisions described above would cause the Fund to be engaged in the business of underwriting, the policy in (5) above will be interpreted not to prevent the Fund from engaging in transactions involving the acquisition or disposition of portfolio securities, regardless of whether the Fund may be considered to be an underwriter under the Securities Act or is otherwise engaged in the underwriting business to the extent permitted by applicable law.

With respect to the fundamental policy relating to lending set forth in (7) above, the Investment Company Act does not prohibit the Fund from making loans (including lending its securities); however, Commission staff interpretations currently prohibit funds from lending more than one-third of their total assets (including lending its securities), except through the purchase of debt obligations or the use of repurchase agreements. In addition, collateral arrangements with respect to options, forward currency and futures transactions and other derivative instruments (as applicable), as well as delays in the settlement of securities transactions, will not be considered loans.

Under its non-fundamental investment restrictions, which may be changed by the Board of Trustees without shareholder approval, the Fund may not:

a. Purchase securities of other investment companies, except to the extent permitted by the Investment Company Act. As a matter of policy, however, the Fund will not purchase shares of any registered open-end investment company or registered unit investment trust, in reliance on Section 12(d)(1)(F) or (G) (the “fund of funds” provisions) of the Investment Company Act, at any time the Fund has knowledge that its shares are purchased by another investment company investor in reliance on the provisions of subparagraph (G) of Section 12(d)(1).

b. Make short sales of securities or maintain a short position, except to the extent permitted by the Fund’s Prospectus and Statement of Additional Information, as amended from time to time, and applicable law.

Unless otherwise indicated, all limitations under the Fund’s fundamental or non-fundamental investment restrictions apply only at the time that a transaction is undertaken. Any change in the percentage of the Fund’s assets invested in certain securities or other instruments resulting from market fluctuations or other changes in the Fund’s total assets will not require the Fund to dispose of an investment until BlackRock determines that it is practicable to sell or close out the investment without undue market or tax consequences.

Shareholders should retain this Supplement for future reference.

SAI-LHE-1221SUP

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