Form SCHEDULE 13D/A MASIMO CORP Filed by: Politan Capital Management LP

Item 4 is hereby amended and supplemented as follows: On June 10, 2026 (the "Closing Date"), the Merger was consummated pursuant to the Merger Agreement. At the effective time of the Merger (the "Effective Time"), Merger Sub merged with and into the Issuer, with the Issuer continuing as the surviving corporation and a wholly owned subsidiary of Parent. At the Effective Time, each share of Common Stock issued and outstanding immediately prior to the Effective Time (other than shares excluded or treated as described in the Merger Agreement) was automatically cancelled, extinguished and converted into the right to receive an amount in cash equal to $180.00 per share, without interest and less any applicable withholding taxes (the "Per Share Merger Consideration"). Accordingly, the 4,590,873 shares of Common Stock beneficially owned by the Reporting Persons immediately prior to the Effective Time were converted into the right to receive the Per Share Merger Consideration. In addition, the 1,119 restricted share units held by Mr. Koffey, as a non-employee director of the Issuer, were cancelled and converted at the Effective Time into the right to receive an amount in cash equal to the Per Share Merger Consideration for each share of Common Stock underlying such restricted share units. As a result of the Merger, the Reporting Persons ceased to beneficially own any shares of Common Stock.

Item 5(a) is hereby amended and restated in its entirety as follows: As a result of the consummation of the Merger, as described in Item 4, each Reporting Person ceased to beneficially own any shares of Common Stock. See rows (11) and (13) of the cover pages to this Amendment No. 17, which reflect zero shares of Common Stock and 0.0% beneficially owned by each Reporting Person.

Item 5(b) is hereby amended and restated in its entirety as follows: (b) See rows (7) through (10) of the cover pages to this Amendment No. 17. Each Reporting Person has no sole or shared power to vote or to direct the vote, and no sole or shared power to dispose or to direct the disposition, of any shares of Common Stock.

Item 5(c) is hereby amended and restated in its entirety as follows: Except as set forth in Item 4, which is incorporated herein by reference, the Reporting Persons have not effected any transactions in the Common Stock during the past sixty (60) days.

June 10, 2026

Item 6 is hereby amended and restated as follows: The information provided or incorporated by reference in Item 4 is hereby incorporated by reference herein.