Specimen Unit Certificate

Exhibit 4.1

SPECIMEN UNIT CERTIFICATE

CUSIP [•]

UNITS CONSISTING OF ONE CLASS A ORDINARY SHARE AND ONE-FIFTH OF ONE REDEEMABLE

WARRANT TO PURCHASE ONE CLASS A ORDINARY SHARE

This Certifies that      is the owner of      Units.

Each Unit (“Unit”) consists of one (1) Class A ordinary share, par value $0.0001 per share (“Ordinary Shares”), of Oaktree Acquisition Corp. III Life Sciences, a Cayman Islands exempted company (the “Company”), and one-fifth (1/5) of one redeemable warrant (each whole warrant, a “Warrant”). Each Warrant entitles the holder to purchase one (1) Ordinary Share for $11.50 per share (subject to adjustment). Each Warrant will become exercisable thirty (30) days after the Company’s completion of a merger, share exchange, asset acquisition, share purchase, reorganization or other similar business combination with one or more businesses (each, a “Business Combination”), and will expire unless exercised before 5:00 p.m., New York City Time, on the date that is five (5) years after the date on which the Company completes its initial Business Combination, or earlier upon redemption or liquidation (the “Expiration Date”). The Ordinary Shares and Warrants comprising the Units represented by this certificate are not transferable separately prior to      , 2024, unless Jefferies LLC, Citigroup Global Markets Inc. and UBS Securities LLC elects to allow earlier separate trading, subject to the Company’s filing with the U.S. Securities and Exchange Commission of a Current Report on Form 8-K containing an audited balance sheet reflecting the Company’s receipt of the gross proceeds of the initial public offering and issuing a press release announcing when separate trading will begin. No fractional warrants will be issued upon separation of the Units and only whole warrants are exercisable. The terms of the Warrants are governed by a Warrant Agreement, dated as of      , 2024, between the Company and Continental Stock Transfer & Trust Company, as Warrant Agent, and are subject to the terms and provisions contained therein, all of which terms and provisions the holder of this certificate consents to by acceptance hereof. Copies of the Warrant Agreement are on file at the office of the Warrant Agent at 1 State Street, 30th Floor, New York, New York 10004, and are available to any Warrant holder on written request and without cost.

Upon the consummation of the Business Combination, the Units represented by this certificate will automatically separate into the Class A Ordinary Shares and Warrants comprising such Units.

This certificate is not valid unless countersigned by the Transfer Agent and Registrar of the Company.

This certificate shall be governed by and construed in accordance with the internal laws of the State of New York.

Witness the facsimile signatures of its duly authorized officers

Oaktree Acquisition Corp. III Life Sciences

The Company will furnish without charge to each unitholder who so requests, a statement of the powers, designations, preferences and relative, participating, optional or other special rights of each class of shares or series thereof of the Company and the qualifications, limitations, or restrictions of such preferences and/or rights.

The following abbreviations, when used in the inscription on the face of this certificate, shall be construed as though they were written out in full according to applicable laws or regulations:

Additional abbreviations may also be used though not in the above list.

For value received,      hereby sells, assigns and transfers unto                   

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(PLEASE INSERT SOCIAL SECURITY OR OTHER IDENTIFYING NUMBER(S) OF ASSIGNEE(S))

(PLEASE PRINT OR TYPEWRITE NAME(S) AND ADDRESS(ES), INCLUDING ZIP CODE, OF ASSIGNEE(S))

    Units represented by the within Certificate, and does hereby irrevocably constitutes and appoints      Attorney to transfer the said shares on the books of the within named Company with full power of substitution in the premises.

In each case, as more fully described in the Company’s final prospectus dated     , 2024, the holder(s) of this certificate with respect to the Ordinary Share included in each Unit, shall be entitled to receive a pro-rata portion of certain funds held in the trust account established in connection with the Company’s initial public offering only in the event that (i) the Company redeems the Ordinary Shares sold in its initial public offering and liquidates because it does not consummate an initial

business combination within the period of time set forth in the Company’s amended and restated memorandum and articles of association, as the same may be amended from time to time, (ii) the Company redeems the Ordinary Shares sold in its initial public offering in connection with a shareholder vote to amend the Company’s amended and restated memorandum and articles of association (A) that would modify the substance or timing of the Company’s obligation to provide holders of the Ordinary Shares the right to have their shares redeemed in connection with the Company’s initial business combination or to redeem 100% of the Ordinary Shares if the Company does not complete its initial business combination within the time period set forth therein or (B) with respect to any other provision relating to the rights of holders of the Ordinary Shares, or (iii) if the holder(s) seek(s) to redeem for cash his, her or its respective Ordinary Shares in connection with a tender offer (or proxy solicitation, solely in the event the Company seeks shareholder approval of the proposed initial business combination) setting forth the details of a proposed initial business combination. In no other circumstances shall the holder(s) have any right or interest of any kind in or to the trust account.