Barry Rosenstein
JANA Partners · Event-driven activist Runs an event-driven activist book, taking stakes in companies it views as undervalued and agitating for strategic changes such as sales, spin-offs, or board seats.
Barry Rosenstein is the founder and managing partner of JANA Partners, an activist hedge fund he founded in 2001 that specializes in event-driven investing.
Showing all 10 reported 13(f) positions; TradingPilot links only the 0 matching its curated universe — a licensed CUSIP↔ticker database was not used. Unmapped positions render as plain text, exactly as filed.
Portfolio allocation (reported 13F equity)
Long US-listed equity positions only; options excluded.
- MERCURY SYS INC25.5%
- COOPER COS INC13.5%
- STATE STR SPDR S&P 500 ETF T13.5%
- LAMB WESTON HLDGS INC12.2%
- FISERV INC9.4%
- MARKEL GROUP INC7.9%
- ALKAMI TECHNOLOGY INC6.4%
- SIX FLAGS ENTERTAINMENT CORP4.6%
- EVERPURE INC4.1%
- RAPID7 INC2.9%
Reported 13F equity value — not a return, not AUM
Long US-listed equity positions only; filed with a ~45-day lag.
| # | Ticker | Security (as filed) | % of 13F | Shares | Reported price | Current | Value | Activity |
|---|---|---|---|---|---|---|---|---|
| 1 | — | MERCURY SYS INC | 25.5% | 3,958,849 | $122.33 | — | $484.3M | New |
| 2 | — | COOPER COS INC | 13.5% | 3,582,480 | $71.71 | — | $256.9M | New |
| 3 | — | STATE STR SPDR S&P 500 ETF T | 13.5% | 342,965 | $746.77 | — | $256.1M | New |
| 4 | — | LAMB WESTON HLDGS INC | 12.2% | 5,394,635 | $43.18 | — | $232.9M | New |
| 5 | — | FISERV INC | 9.4% | 3,662,080 | $49.05 | — | $179.6M | New |
| 6 | — | MARKEL GROUP INC | 7.9% | 76,743 | $1,953.01 | — | $149.9M | New |
| 7 | — | ALKAMI TECHNOLOGY INC | 6.4% | 6,747,707 | $18.12 | — | $122.3M | New |
| 8 | — | SIX FLAGS ENTERTAINMENT CORP | 4.6% | 4,116,099 | $21.30 | — | $87.7M | New |
| 9 | — | EVERPURE INC | 4.1% | 989,196 | $78.79 | — | $77.9M | Trimmed −5% |
| 10 | — | RAPID7 INC | 2.9% | 6,749,936 | $8.10 | — | $54.7M | New |
Reported price = value ÷ shares at the quarter-end — an average, NOT the manager's buy/sell price.
Current shows the stock's price change since the filing quarter-end (mapped names only) — it is the STOCK's move, not the manager's realized return (we don't know their cost basis or whether they still hold).
TradingPilot analysis of the reported 13F equity book
As of 2026Q2, Barry Rosenstein's reported 13F book holds 10 equity positions; the top 5 are 74% of it.
- MERCURY SYS INC — 25.5% of 13F
- COOPER COS INC — 13.5% of 13F
- STATE STR SPDR S&P 500 ETF T — 13.5% of 13F
- LAMB WESTON HLDGS INC — 12.2% of 13F
- FISERV INC — 9.4% of 13F
This quarter: 9 new, 0 added, 1 trimmed, 0 sold out.
- EVERPURE INC — Trimmed (−53,100 sh)