Magnite, Inc.
US ˙ NasdaqGS ˙ US55955D1000

SecurityMGNI / Magnite, Inc.
InstitutionSimplex Trading, Llc
Latest Disclosed Ownership11,316 shares
Latest Disclosed Value $ 134,434
Simplex Trading, Llc ownership in MGNI / Magnite, Inc.

On May 14, 2026 - Simplex Trading, Llc filed a 13F-HR form disclosing ownership of 11,316 shares of Magnite, Inc. (US:MGNI) valued at $134,434 USD as of March 31, 2026. The entity filed a previous 13F-HR on February 11, 2026 disclosing 263,362 shares of Magnite, Inc.. This represents a change in shares of -95.70% during the quarter. The current value of the position is $163,516 USD.

Simplex Trading, Llc has a history of taking positions in derivatives of the underlying security (MGNI) in the form of stock options. The firm currently holds call options representing 27,100 of underlying shares valued at $321,948 USD and put options representing 15,600 of underlying shares valued at $185,328 USD .

Note: prior versions of this page mistakenly stated that the share values represented the number of options, not the number of underlying shares. For more information on the data backing these reports, please see the SEC document Frequently Asked Questions About Form 13F.

Institutional Ownership: 13F and NPORT Filings

The Security and Class in the table below are shown exactly as filed by the investor. We do our best to track continuity of investments through acquisitions, and this will be reflected in the table as changes in names. In addition to descriptive data, performance of the investment is shown over time. To calculate quarterly performance, we first calculate cost basis of the shares purchased during the quarter, then use that to calculate gross profit. Quarterly return is Gross Profit / Starting Portfolio value.

Note that cost basis is calculated and stored in thousands, so small quarterly changes in shares frequently result in a cost basis of zero.

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Institutional Put/Call Ratios
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In addition to reporting standard equity and debt issues, institutions with more than 100MM assets under management must also disclose their put and call option holdings. Since put options generally indicate negative sentiment, and call options indicate positive sentiment, we can get a sense of the overall institutional sentiment by plotting the ratio of puts to calls. The chart to the right plots the historical put/call ratio for this instrument.

Using Put/Call Ratio as an indicator of investor sentiment overcomes one of the key deficiencies of using total institutional ownership, which is that a significant amount of assets under management are invested passively to track indices. Passively-managed funds do not typically buy options, so the put/call ratio indicator more closely tracks the sentiment of actively-managed funds.

MGNI / Magnite, Inc. Historical Put/Call Ratio
Disclosed Equity Positions (from 13F/NPORT Filings)
File
Date
Effective
Date
Form Security Class ID Avg Price
Paid (Est)
Reported
Shares
ΔShares ΔShares
(%)
Reported
Value
(x1000)
ΔValue
(%)
Alloc
(%)
ΔAlloc ΔAlloc (%) Cost Basis
(x1000)
Unrealized
Gain/Loss
(x1000)
2026-05-14 2026-03-31 13F MAGNITE COM 55955D100 11,316 -252,046 -95.70 134 -96.86 0.0000
2026-02-11 2025-12-31 13F MAGNITE COM 55955D100 263,362 146,317 125.01 4,274 213,600.00 0.0024
2025-11-12 2025-09-30 13F MAGNITE COM 55955D100 117,045 64,211 121.53 3 100.00 0.0013
2025-08-05 2025-06-30 13F MAGNITE COM 55955D100 52,834 52,834 1 0.0007
2025-05-12 2025-03-31 13F MAGNITE COM 55955D100 0 -31,987 -100.00 0 0.0000
2025-02-11 2024-12-31 13F MAGNITE COM 55955D100 31,987 -56,172 -63.72 1 -100.00 0.0003
2024-11-08 2024-09-30 13F MAGNITE COM 55955D100 88,159 80,635 1,071.70 1 0.0007
2024-07-25 2024-06-30 13F MAGNITE COM 55955D100 7,524 7,524 0 0.0001
2023-11-01 2023-09-30 13F MAGNITE COM 55955D100 0 -24,057 -100.00 0 0.0000
2023-08-04 2023-06-30 13F MAGNITE COM 55955D100 24,057 12,330 105.14 0 0.0003
2023-04-27 2023-03-31 13F MAGNITE COM 55955D100 11,727 -27,701 -70.26 0 0.0001
2023-02-02 2022-12-31 13F MAGNITE COM 55955D100 39,428 39,428 0 0.0005
2022-11-04 2022-09-30 13F MAGNITE COM 55955D100 0 -30,590 -100.00 0 -100.00
2022-08-03 2022-06-30 13F MAGNITE COM 55955D100 30,590 -27,180 -47.05 271 -64.48 0.0003
2022-05-02 2022-03-31 13F MAGNITE COM 55955D100 57,770 -17,703 -23.46 763 -42.20 0.0007
2022-02-23 2021-12-31 13F/A-1 MAGNITE COM 55955D100 75,473 75,473 1,320 0.0013
2021-08-12 2021-06-30 13F MAGNITE COM 55955D100 0 -49,469 -100.00 0 -100.00
2021-04-26 2021-03-31 13F MAGNITE COM 55955D100 49,469 14,173 40.15 2,058 90.03 0.0037
2021-02-02 2020-12-31 13F MAGNITE COM 55955D100 35,296 -10,009 -22.09 1,083 244.90 0.0014
2020-10-14 2020-09-30 13F MAGNITE COM 55955D100 45,305 45,305 314 0.0004
Disclosed Call Options
File
Date
Effective
Date
Form Security Class ID Opt Avg Share
Price
Shares ΔShares
(%)
Value
(x1000)
ΔValue
(%)
Prior Allocation
(%)
Allocation
(%)
ΔAllocation
(%)
Cost Basis
(x1000)
Profit
(x1000)
Return
(%)
2026-05-14 2026-03-31 13F MAGNITE CALL Call 27,100 -90.22 322 -92.86 n/a n/a n/a
2026-02-11 2025-12-31 13F MAGNITE CALL Call 277,100 -24.31 4,497 64,142.86 n/a n/a n/a
2025-11-12 2025-09-30 13F MAGNITE CALL Call 366,100 34.65 8 16.67 n/a n/a n/a
2025-08-05 2025-06-30 13F MAGNITE CALL Call 271,900 9.15 7 200.00 n/a n/a n/a
2025-05-12 2025-03-31 13F MAGNITE CALL Call 249,100 -37.52 3 -66.67 n/a n/a n/a
2025-02-11 2024-12-31 13F MAGNITE CALL Call 398,700 -10.46 6 0.00 n/a n/a n/a
2024-11-08 2024-09-30 13F MAGNITE CALL Call 445,300 115.75 6 200.00 n/a n/a n/a
2024-07-25 2024-06-30 13F MAGNITE CALL Call 206,400 52.66 3 100.00 n/a n/a n/a
2024-04-25 2024-03-31 13F MAGNITE CALL Call 135,200 -53.65 1 -50.00 n/a n/a n/a
2024-02-02 2023-12-31 13F MAGNITE CALL Call 291,700 -1.78 3 0.00 n/a n/a n/a
2023-11-01 2023-09-30 13F MAGNITE CALL Call 297,000 110.94 2 100.00 n/a n/a n/a
2023-08-04 2023-06-30 13F MAGNITE CALL Call 140,800 92.61 2 n/a n/a n/a
2023-04-27 2023-03-31 13F MAGNITE CALL Call 73,100 -56.77 1 -100.00 n/a n/a n/a
2023-02-02 2022-12-31 13F MAGNITE CALL Call 169,100 -30.07 2 -99.94 n/a n/a n/a
2022-11-04 2022-09-30 13F MAGNITE CALL Call 241,800 21.69 1,588 -9.98 n/a n/a n/a
2022-08-03 2022-06-30 13F MAGNITE CALL Call 198,700 -11.14 1,764 -40.26 n/a n/a n/a
2022-05-02 2022-03-31 13F MAGNITE CALL Call 223,600 44.72 2,953 9.25 n/a n/a n/a
2022-02-23 2021-12-31 13F/A MAGNITE CALL Call 154,500 21.65 2,703 -38.62 n/a n/a n/a
2022-02-04 2021-12-31 13F MAGNITE CALL Call 127,000 4,404 n/a n/a n/a
2021-10-28 2021-09-30 13F MAGNITE CALL Call 127,000 1.20 4,404 3.72 n/a n/a n/a
2021-08-12 2021-06-30 13F MAGNITE CALL Call 125,500 8,549.21 4,246 -29.67 n/a n/a n/a
2021-04-26 2021-03-31 13F MAGNITE CALL Call 1,451 20.72 6,037 63.56 n/a n/a n/a
2021-02-02 2020-12-31 13F MAGNITE CALL Call 1,202 245.40 3,691 1,431.54 n/a n/a n/a
2020-10-14 2020-09-30 13F MAGNITE CALL Call 348 241 n/a n/a n/a
Disclosed Put Options
File
Date
Effective
Date
Form Security Class ID Opt Avg Share Price Shares ΔShares
(%)
Value
(x1000)
ΔValue
(%)
Prior Allocation
(%)
Allocation
(%)
ΔAllocation
(%)
Cost Basis
(x1000)
Profit
(x1000)
Return
(%)
2026-05-14 2026-03-31 13F MAGNITE PUT Put 15,600 -90.77 185 -93.26 n/a n/a n/a
2026-02-11 2025-12-31 13F MAGNITE PUT Put 169,100 -8.45 2,744 68,500.00 n/a n/a n/a
2025-11-12 2025-09-30 13F MAGNITE PUT Put 184,700 2.21 4 0.00 n/a n/a n/a
2025-08-05 2025-06-30 13F MAGNITE PUT Put 180,700 113.85 4 n/a n/a n/a
2025-05-12 2025-03-31 13F MAGNITE PUT Put 84,500 -5.16 1 -100.00 n/a n/a n/a
2025-02-11 2024-12-31 13F MAGNITE PUT Put 89,100 66.54 1 n/a n/a n/a
2024-11-08 2024-09-30 13F MAGNITE PUT Put 53,500 -46.77 1 -100.00 n/a n/a n/a
2024-07-25 2024-06-30 13F MAGNITE PUT Put 100,500 206.40 1 n/a n/a n/a
2024-04-25 2024-03-31 13F MAGNITE PUT Put 32,800 -25.45 0 n/a n/a n/a
2024-02-02 2023-12-31 13F MAGNITE PUT Put 44,000 10.00 0 n/a n/a n/a
2023-11-01 2023-09-30 13F MAGNITE PUT Put 40,000 128.57 0 n/a n/a n/a
2023-08-04 2023-06-30 13F MAGNITE PUT Put 17,500 -60.32 0 n/a n/a n/a
2023-04-27 2023-03-31 13F MAGNITE PUT Put 44,100 184.52 0 n/a n/a n/a
2023-02-02 2022-12-31 13F MAGNITE PUT Put 15,500 -58.33 0 -100.00 n/a n/a n/a
2022-11-04 2022-09-30 13F MAGNITE PUT Put 37,200 -32.85 244 -50.31 n/a n/a n/a
2022-08-03 2022-06-30 13F MAGNITE PUT Put 55,400 -14.90 491 -42.84 n/a n/a n/a
2022-05-02 2022-03-31 13F MAGNITE PUT Put 65,100 -29.85 859 -47.11 n/a n/a n/a
2022-02-23 2021-12-31 13F/A MAGNITE PUT Put 92,800 89.00 1,624 -4.58 n/a n/a n/a
2022-02-04 2021-12-31 13F MAGNITE PUT Put 49,100 1,702 n/a n/a n/a
2021-10-28 2021-09-30 13F MAGNITE PUT Put 49,100 1.03 1,702 3.53 n/a n/a n/a
2021-08-12 2021-06-30 13F MAGNITE PUT Put 48,600 5,342.33 1,644 -55.75 n/a n/a n/a
2021-04-26 2021-03-31 13F MAGNITE PUT Put 893 14.49 3,715 55.11 n/a n/a n/a
2021-02-02 2020-12-31 13F MAGNITE PUT Put 780 1,757.14 2,395 8,158.62 n/a n/a n/a
2020-10-14 2020-09-30 13F MAGNITE PUT Put 42 29 n/a n/a n/a
Legend
Shares
The total number of shares held by the institution at the end of the reporting period (the effective date). This is provided in the filing.
Value
The total value of the shares as of the effective date. This is provided in the filing.
Avg. Share Price
The weighted average share price of the shares held by the institution. We use FIFO accounting to determine this price
Class
This is the security class as indicated by the filer. There are a variety of values for this field. Common values include "EC" = equity common, "EP" - equity preferred
Allocation (%)
The percent of the institution's portfolio that this position represents. This is provided in NPORT filings. For 13F filings, we calculate it.
Change in Allocation
The change in allocation from the prior reporting period. This is calculated as current allocation - prior allocation.
Change in Allocation (%)
The percent change in allocation from the prior reporting period. This is calculated as (current allocation - prior allocation) / prior allocation.
Cost Basis
The total cost of the shares held. This is calculated as reported shares * avg. share price
Unrealized Gain/Loss
This is the market value of the position as of the effective date minus the cost basis.