Magnetar Financial LLC reported * MASIMO CORP COM (MASI) in 10 quarterly 13F filings from 2025 Q4 through 2026 Q1. Peak portfolio weight reached 0.77% in 2026 Q1. The latest visible filing shows MASI at 0.77% of the fund.
This page tracks quarterly shares, estimated market value, portfolio weight, filing dates, and disclosure-aligned stock prices directly from SEC EDGAR 13F filings. Older history is available after unlock; the visible window still shows the most recent pattern.
This page is designed to answer the real investor question behind a 13F filing: how meaningful was Magnetar Financial LLC's position in * MASIMO CORP COM, and how did that conviction change over time? You can read the holding window, peak weight, latest reported size, disclosure timing, and quarter-by-quarter changes without piecing the story together from raw SEC rows.
MASI was reported at 0.77% of portfolio in the most recent visible filing.
Peak weight helps separate a token disclosure from a real conviction holding the fund genuinely cared about.
Longer holding windows often tell a very different story from short-lived tactical trades or one-quarter experiments.
Knowing that a fund owned a stock is useful. Knowing whether it was a 0.20% placeholder or a true high-conviction position is where the signal actually starts.
As of 2026 Q1 — sorted by position size
These are the practical questions this page is built to answer before you even open the full history table.
Magnetar Financial LLC reported MASI across 2 quarterly 13F filings, from 2025 Q4 through 2026 Q1.
The largest reported portfolio weight for MASI was 0.77% in 2026 Q1.
The most recent filing on this page is 2026 Q1, when Magnetar Financial LLC reported 427,081 shares, equal to 0.77% of portfolio, with an estimated market value of $76.0M.
The chart compares Magnetar Financial LLC's quarterly MASI portfolio weight with the stock's indexed share price, so you can see whether the fund was building, trimming, or holding the position as price moved.
Based on 13F filing dates vs. subsequent MASI price moves, Magnetar Financial LLC correctly timed 4 out of 9 reported position changes (44%). The annualised alpha on MASI relative to SPY over the holding period was -59.7%.