Prospectus Supplement

John Hancock Marathon Asset-Based Lending Fund (the “Fund”)

Supplement dated August 29, 2025, to the current Prospectus, as may be supplemented (the “Prospectus”)

Reference is made to the Prospectus Supplement, dated July 9, 2025 (the “July Supplement”), of the Fund. The shareholder meeting related to the approval of the conversion of the Fund to an interval fund as well as certain related matters scheduled for October 9, 2025 will not be held on that date, and, accordingly, the Fund will not convert to an interval fund on or around November 18, 2025. A shareholder meeting relating to the interval fund conversion is expected to be rescheduled on a date sometime in the first quarter of 2026, with implementation of the conversion expected to take place as soon thereafter as practicable following shareholder approval.

The following changes discussed in the July Supplement remain in effect:

Other Changes to the Fund’s Current Prospectus

Effective after the close of business on or about August 1, 2025, Class S shares and Class D shares will stop accepting orders from new investors to purchase shares. Existing investors may make subsequent purchases to their existing accounts.

In addition, effective immediately, the below disclosure in the Prospectus will be deleted:

“Eligible Investors

Shares will be offered only to Eligible Investors. This means that to purchase Shares of the fund, a prospective Shareholder will be required to certify that the Shares are being acquired by an investor who either: (i) an “accredited investor” as defined in Rule 501(a) of Regulation D promulgated under the 1933 Act; or (ii) a “non-U.S. Person” investor within the meaning of Regulation S under the 1933 Act. Except as otherwise provided, shares of a fund generally may be sold only to U.S. citizens, U.S. residents, and U.S. domestic corporations, partnerships, trusts or estates. For purposes of this policy, U.S. citizens and U.S. residents must reside in the U.S. and U.S. domestic corporations, partnerships, trusts, and estates must have a U.S. address of record. Eligible Investors also include investment companies and U.S. and foreign feeder funds in compliance with the 1940 Act. Existing Investors seeking to purchase additional Shares will be required to qualify as Eligible Investors at the time of the additional purchase, except with respect to reinvested distributions. The Advisor may from time to time impose stricter or less stringent eligibility requirements.”

Similarly, effective immediately, the section titled “Eligible Investors” under the sub-heading “INVESTING IN THE FUND” in the “Prospectus Summary” section of the Prospectus is deleted in its entirety. Also, effective immediately, all other references to “Eligible Investors” in the Prospectus will be deleted.

Moreover, the eighth paragraph in the “PURCHASE TERMS” section of the Prospectus will be updated by adding four new additional sentences, as follows:

“All Shares are sold at the most recently calculated net asset value per Share for a particular class as of the date on which the purchase is accepted. The minimum initial investment in the fund by any account is as follows: $1 million for Class I Shares with additional investment minimums of $100,000; and $10,000 with additional investment minimums of $5,000 for Class S Shares and Class D Shares. The fund may accept investments for a lesser amount under certain circumstances at its sole discretion. Investors that are employees of the Advisor or its affiliates are eligible to invest in Shares and may be subject to lower minimum investments than other investors. Certain selling brokers, dealers or banks and financial advisors may impose higher or lower minimum investment levels or other requirements than those imposed by the fund. Except

as otherwise provided, shares of the fund generally may be sold only to U.S. citizens, U.S. residents, and U.S. domestic corporations, partnerships, trusts or estates. For purposes of this policy, U.S. citizens and U.S. residents must reside in the U.S. and U.S. domestic corporations, partnerships, trusts, and estates must have a U.S. address of record. Shares of the fund may also be sold to investment companies and U.S. and foreign feeder funds in compliance with the 1940 Act. The Advisor may from time to time impose stricter or less stringent eligibility requirements.”

Finally, effective immediately, the section of the Prospectus “PURCHASE TERMS” on pages 48 – 51 is amended to add the following disclosure after the sixth paragraph:

“The fund has authorized one or more financial intermediaries to receive on its behalf purchase and repurchase orders. The fund will be deemed to have received a purchase or repurchase order when an authorized financial intermediary or, if applicable, a financial intermediary’s authorized designee, receives the order. A purchase order will be priced at the appropriate price next computed after it is received in “good order” by a financial intermediary (or, if applicable, such financial intermediary’s authorized designee). The definition of “good order” may vary among financial intermediaries.

Financial Intermediary-Requested Intra-Fund Exchanges: Financial intermediaries may, in connection with a change in a client’s account type or otherwise in accordance with a financial intermediary’s policies and procedures, request, on behalf of the intermediary’s clients, that the fund exchange Shares of one class of Shares of the fund held by such clients for Shares of another class of Shares of the fund. Any such exchange will not be subject to a sales charge. The fund will only complete such an exchange at the request of a financial intermediary and without making inquiry as to whether the exchange is consistent with the particular intermediary’s policies and procedures or the client’s account type and/or suitability criteria (but subject to the client otherwise meeting the criteria for investment in the target class of Shares as set forth herein). An investor should contact his or her financial intermediary to learn more about the details of this exchange feature and whether and under what circumstances it may apply in accordance with the investor’s arrangements with the particular intermediary.

Shares of one class of the fund will be exchanged for Shares of a different class of the fund on the basis of their respective NAVs. Ongoing fees and expenses incurred by a given Share class will differ from those of other Share classes, and a Shareholder receiving new Shares in an intra-fund exchange may be subject to higher or lower total expenses following such exchange.”

You should read this supplement in conjunction with the Prospectus and retain it for your future reference.

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