Ticker · CUSIP 74765K105

QSI

QUANTUM SI INC

Healthcare·Medical Devices

···Share

Holders (tracked)

Combined shares

12,273,815

Combined value

$13.50M

Last close

$1.07

Quarter

2025Q4

Price is -2.7% vs the avg quarter-end implied price across tracked holders.

Price · 1Y$1.07-0.08 (-6.96%)H $2.63 · L $0.71 · Avg Vol 7.5M

Position opened

Tracked holders · last 8 quarters

Flat over the last 8 quarters.

SEC event timeline

12 events

Ken Griffin (Citadel Advisors) added2026-02-17
+2,269,050 shares · 2025Q4
Position
Izzy Englander (Millennium Mgmt) trimmed2026-02-17
−2,478,168 shares · 2025Q4
Position
T. Rowe Price added2026-02-17
+4,452 shares · 2025Q4
Position
AQR Capital Management added2026-02-17
+2,865 shares · 2025Q4
Position
Two Sigma Investments added2026-02-17
+868,329 shares · 2025Q4
Position
Cathie Wood (ARK Invest) trimmed2026-02-11
−602,471 shares · 2025Q4
Position
AQR Capital Management trimmed2025-11-14
−37,879 shares · 2025Q3
Position
Izzy Englander (Millennium Mgmt) trimmed2025-11-14
−1,109,300 shares · 2025Q3
Position
Two Sigma Investments trimmed2025-11-14
−48,590 shares · 2025Q3
Position
T. Rowe Price trimmed2025-11-14
−28,472 shares · 2025Q3
Position
Renaissance Technologies exited2025-11-13
−89,200 shares · 2025Q3
Position
Cathie Wood (ARK Invest) trimmed2025-11-12
−336,694 shares · 2025Q3
Position

Insider activity

No insider transactions in the last 30 days.

View full insider history for QSI →

Follow-the-investor returns

If you'd copied each holder of QSI…

Cost basis inferred from each manager's quarter-over-quarter position changes. Sorted by % return on the position they're still holding.

Investor	First in	Cost basis	Return	Position value today
Ken Griffin (Citadel Advisors)	2021Q2	$1.16	-7.6%	$595K
Ken Griffin (Citadel Advisors)	2021Q2	$1.16	-7.6%	$595K
Ken Griffin (Citadel Advisors)	2021Q2	$1.16	-7.6%	$595K
Two Sigma Investments	2022Q4	$1.21	-11.3%	$1.5M
Izzy Englander (Millennium Mgmt)	2021Q2	$1.22	-12.1%	$205K
AQR Capital Management	2022Q1	$2.55	-58.1%	$93K
T. Rowe Price	2021Q2	$4.57	-76.6%	$103K
Cathie Wood (ARK Invest)	2021Q2	$7.41	-85.6%	$7.5M

Who moved on this name in 2025Q4

Position changes reported for the latest quarter, grouped by direction.

New positions0

—

Added to4

Ken Griffin (Citadel Advisors)
+2,269,050
$2.5M
Two Sigma Investments
+868,329
$955K
AQR Capital Management
+2,865
$3K
T. Rowe Price
+4,452
$5

Trimmed2

Izzy Englander (Millennium Mgmt)
−2,478,168
$2.7M
Cathie Wood (ARK Invest)
−602,471
$663K

Exited0

—

Institutional ownership over time

Distinct super-investors holding this ticker · combined dollar value, by quarter.

Quarter	Holders	Shares	Combined value	Δ holders
2022Q1	10	22,781,181	$106.6M	—
2022Q2	9	25,992,280	$87.1M	-1
2022Q3	8	25,162,218	$69.2M	-1
2022Q4	11	23,186,461	$42.4M	+3
2023Q1	12	22,446,781	$39.5M	+1
2023Q2	10	22,807,157	$40.8M	-2
2023Q3	6	21,841,982	$36.3M	-4
2023Q4	7	23,341,996	$46.9M	+1
2024Q1	8	20,581,741	$40.5M	+1
2024Q2	9	20,241,728	$21.3M	+1
2024Q3	9	12,326,904	$10.9M	—
2024Q4	7	10,822,901	$29.2M	-2
2025Q1	9	15,498,731	$18.6M	+2
2025Q2	9	13,967,253	$27.4M	—
2025Q3	8	12,183,158	$17.2M	-1
2025Q4	8	12,273,815	$13.5M	—

Who owns QSI

8 super-investors · 2025Q4

Tracked stake

12.27M

Combined value

$14M

% of shares outstanding

—

shares-out unknown

Quarter action mix

Added6Trim2

#	Manager	Shares	Value	% of book	Last action
1	Cathie Wood ARK Invest	7.02M	$8M	0.1%	Trim−602.5K
2	Ken Griffin Citadel Advisors	2.68M	$3M	0.0%	Added+2.27M
3	Two Sigma Investments	1.38M	$2M	0.0%	Added+868.3K
4	Ken Griffin Citadel Advisors	556.0K	$612K	0.0%	Added+2.27M
5	Ken Griffin Citadel Advisors	261.0K	$287K	0.0%	Added+2.27M
6	Izzy Englander Millennium Mgmt	191.8K	$211K	0.0%	Trim−2.48M
7	T. Rowe Price	96.5K	$107K	0.0%	Added+4.5K
8	AQR Capital Management	86.7K	$95K	0.0%	Added+2.9K

Recent moves

20 transactions

ADDAQR Capital Management
+2,865 · 2025Q4
TRIMIzzy Englander (Millennium Mgmt)
−2,478,168 · 2025Q4
ADDKen Griffin (Citadel Advisors)
+2,269,050 · 2025Q4
ADDT. Rowe Price
+4,452 · 2025Q4
ADDTwo Sigma Investments
+868,329 · 2025Q4
TRIMCathie Wood (ARK Invest)
−602,471 · 2025Q4
TRIMT. Rowe Price
−28,472 · 2025Q3
TRIMAQR Capital Management
−37,879 · 2025Q3
TRIMIzzy Englander (Millennium Mgmt)
−1,109,300 · 2025Q3
TRIMTwo Sigma Investments
−48,590 · 2025Q3
SOLDRenaissance Technologies
−89,200 · 2025Q3
TRIMCathie Wood (ARK Invest)
−336,694 · 2025Q3
ADDT. Rowe Price
+12,332 · 2025Q2
TRIMIzzy Englander (Millennium Mgmt)
−155,026 · 2025Q2
TRIMTwo Sigma Investments
−252,533 · 2025Q2
ADDAQR Capital Management
+25,661 · 2025Q2
TRIMRenaissance Technologies
−782,556 · 2025Q2
TRIMCathie Wood (ARK Invest)
−752,765 · 2025Q2
NEWIzzy Englander (Millennium Mgmt)
+3,934,285 · 2025Q1
ADDTwo Sigma Investments
+664,292 · 2025Q1

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