MASON CAPITAL MANAGEMENT LLC — 13F Holdings & Portfolio
CIK 1218735 · latest 13F-HR filed 2026-08-14
MASON CAPITAL MANAGEMENT LLC manages $607.0M in 13F-reported U.S. long-equity assets across 9 reported positions as of its 2026-06-30 13F-HR filing. Its largest disclosed positions are ATS (77.78%), BKD (6.83%), NVRI (6.40%). Quarter over quarter (versus its 2026-03-31 filing) the fund opened 2 new positions and exited 0; 3 existing positions rose in reported value and 2 fell.
AUM is the long-equity portion reported on Form 13F-HR. Excludes short positions, cash, foreign holdings, and non-13F assets. For informational purposes only — not investment advice.
Long-equity book
Distinct positions
Filed 2026-08-14
vs 2026-03-31
Portfolio charts
Latest quarter's book, what changed, and how the portfolio has evolved across filings.
Portfolio map
Q2 26Box size = position value; colour = change in share count vs the prior quarter (green added, red trimmed, blue new). Rows split across managers or share classes are combined. Click a box for the stock.
Sector mix
% of 13F valueSectors from each company's SIC code; funds and ETFs grouped separately.
Biggest buys and sells
Q1 26 → Q2 26Estimated from the change in shares held × the quarter-end price, so price moves alone don't count as buying. New and exited positions are included.
13F assets and positions
4 quartersTotal reported 13F value (bars) and number of positions (line) each quarter. Value changes include market moves.
Top positions over time
reported valueThe eight largest current positions, valued at each quarter end.
Concentration
top 10 = 100%Cumulative share of the portfolio held in the largest N positions.
As of the firm’s regulatory filing dated Mar 31, 2026.
| Name | Title / Status | Ownership | Type |
|---|---|---|---|
| CONSTANTINO, DANIELA Control | ANALYST AND MANAGING MEMBER since Dec 2013 | Less than 5% | Individual |
| CUTINI, MICHAEL, GEORGE Control | GENERAL COUNSEL AND CHIEF COMPLIANCE OFFICER since Mar 2022 | Less than 5% | Individual |
| GARSCHINA, KENNETH, MARIO Control | MANAGING MEMBER AND PRINCIPAL since Jun 2000 | 50–75% | Individual |
| GRIZZETTI, JOHN, CHRISTOPHER Control | CHIEF OPERATING OFFICER AND MANAGING MEMBER since Sep 2002 | Less than 5% | Individual |
| MARTINO, MICHAEL, EMIL Control | MANAGING MEMBER AND PRINCIPAL since Jun 2000 | 50–75% | Individual |
| MASON CAPITAL HOLDINGS LP Control | MANAGING MEMBER since Oct 2009 | Less than 5% | Domestic Entity |
| READ, SAMUEL, THORNTON Control | ANALYST AND MANAGING MEMBER since Jan 2023 | Less than 5% | Individual |
| SATZINGER, DEREK, RYAN Control | CHIEF FINANCIAL OFFICER since Jan 2013 | Less than 5% | Individual |
| GARSCHINA, KENNETH, MARIO Control Indirect owner via MASON CAPITAL HOLDINGS LP | LIMITED PARTNER since Oct 2009 | 50–75% | Individual |
| GARSCHINA, KENNETH, MARIO Control Indirect owner via MASON MANAGEMENT HOLDINGS LLC | MANAGING MEMBER since Oct 2009 | 50–75% | Individual |
| MARTINO, MICHAEL, EMIL Control Indirect owner via MASON CAPITAL HOLDINGS LP | LIMITED PARTNER since Oct 2009 | 50–75% | Individual |
| MARTINO, MICHAEL, EMIL Control Indirect owner via MASON MANAGEMENT HOLDINGS LLC | MANAGING MEMBER since Oct 2009 | 50–75% | Individual |
| MASON MANAGEMENT HOLDINGS LLC Control Indirect owner via MASON CAPITAL HOLDINGS LP | GENERAL PARTNER since Oct 2009 | General partner, trustee or manager | Domestic Entity |
Ownership & leadership changes · 10 filings with changes since Feb 10, 2012
From the firm’s regulatory filings, newest first. Dates are filing dates: a filing that no longer lists someone does not say when they left.
- AddedREAD, SAMUEL, THORNTON · ANALYST AND MANAGING MEMBER · Less than 5% · control person
- No longer listedMCGOVERN, JAMES, MURDOCK · GENERAL COUNSEL AND CHIEF COMPLIANCE OFFICER · Less than 5% · control person · listed since Jul 2018
- AddedCUTINI, MICHAEL, GEORGE · GENERAL COUNSEL AND CHIEF COMPLIANCE OFFICER · Less than 5% · control person
- ChangedMCGOVERN, JAMES, MURDOCK · title CHIEF COMPLIANCE OFFICER → GENERAL COUNSEL AND CHIEF COMPLIANCE OFFICER
- AddedGARSCHINA, KENNETH, MARIO · LIMITED PARTNER · 50–75% · indirect via MASON CAPITAL HOLDINGS LP · control person
- AddedGARSCHINA, KENNETH, MARIO · MANAGING MEMBER · 50–75% · indirect via MASON MANAGEMENT HOLDINGS LLC · control person
- AddedMARTINO, MICHAEL, EMIL · LIMITED PARTNER · 50–75% · indirect via MASON CAPITAL HOLDINGS LP · control person
- AddedMARTINO, MICHAEL, EMIL · MANAGING MEMBER · 50–75% · indirect via MASON MANAGEMENT HOLDINGS LLC · control person
- AddedMASON CAPITAL HOLDINGS LP · MANAGING MEMBER · Less than 5% · control person
- AddedMASON MANAGEMENT HOLDINGS LLC · GENERAL PARTNER · General partner, trustee or manager · indirect via MASON CAPITAL HOLDINGS LP · control person
- ChangedCONSTANTINO, DANIELA · title ANALYST, PARTNER → ANALYST AND MANAGING MEMBER
- ChangedGRIZZETTI, JOHN, CHRISTOPHER · title CHIEF OPERATING OFFICER, PARTNER → CHIEF OPERATING OFFICER AND MANAGING MEMBER
- AddedMCGOVERN, JAMES, MURDOCK · CHIEF COMPLIANCE OFFICER · Less than 5% · control person
- ChangedGRIZZETTI, JOHN, CHRISTOPHER · title CHIEF OPERATING OFFICER, CHIEF COMPLIANCE OFFICER, PARTNER → CHIEF OPERATING OFFICER, PARTNER
- No longer listedSIMMONS, MEREDITH, ANN · CHIEF COMPLIANCE OFFICER · Less than 5% · control person · listed since Feb 2011
- ChangedGRIZZETTI, JOHN, CHRISTOPHER · title CHIEF OPERATING OFFICER, PARTNER → CHIEF OPERATING OFFICER, CHIEF COMPLIANCE OFFICER, PARTNER
- No longer listedDEMARK, ADAM, COURTLAND · ANALYST, PARTNER · Less than 5% · control person · listed since Dec 2006
- No longer listedMACKNIGHT, DAVID, SCOTT · ANALYST, PARTNER · Less than 5% · control person · listed since Aug 2001
- AddedCONSTANTINO, DANIELA · ANALYST, PARTNER · Less than 5% · control person
- AddedSATZINGER, DEREK, RYAN · CHIEF FINANCIAL OFFICER · Less than 5% · control person
- ChangedGRIZZETTI, JOHN, CHRISTOPHER · title CHIEF FINANCIAL OFFICER, PARTNER → CHIEF OPERATING OFFICER, PARTNER
Older changes (1 more filing)
- ListedDEMARK, ADAM, COURTLAND · ANALYST, PARTNER · Less than 5% · control person
- ListedGARSCHINA, KENNETH, MARIO · MANAGING MEMBER AND PRINCIPAL · 50–75% · control person
- ListedGRIZZETTI, JOHN, CHRISTOPHER · CHIEF FINANCIAL OFFICER, PARTNER · Less than 5% · control person
- ListedMACKNIGHT, DAVID, SCOTT · ANALYST, PARTNER · Less than 5% · control person
- ListedMARTINO, MICHAEL, EMIL · MANAGING MEMBER AND PRINCIPAL · 50–75% · control person
- ListedSIMMONS, MEREDITH, ANN · CHIEF COMPLIANCE OFFICER · Less than 5% · control person
Quarter-over-quarter changes
Changes in reported position value vs the prior 13F, so price moves count too, not just shares bought or sold.
Top Adds (vs prior quarter)
- BROOKDALE SENIOR LIVING INC$10.9M +35.6%
- JELD-WEN HOLDING INC$3.7M +384.2%
- READY CAPITAL CORP$561.6K +8.0%
MASON CAPITAL MANAGEMENT LLC Holdings (2026-06-30)
Rows tagged Call or Put are options positions, not stock. Per SEC Form 13F-HR, Value shows the notional value of the underlying (shares covered × underlying price), not the option premium. Shares is the number of underlying shares covered (divide by 100 for contract count).
| # | Issuer | Symbol | CUSIP | Value | Weight | Shares | Type |
|---|---|---|---|---|---|---|---|
| 1 | ATS CORPORATION | ATS | 00217Y104 | $472.1M | 77.78% | 16,404,170 | SH |
| 2 | BROOKDALE SENIOR LIVING INC | BKD | 112463104 | $41.4M | 6.83% | 2,575,826 | SH |
| 3 | ENVIRI CORP | NVRI | 415864107 | $38.9M | 6.40% | 1,770,959 | SH |
| 4 | CLEAR CHANNEL OUTDOOR HLDGS | CCO | 18453H106 | $23.8M | 3.92% | 9,828,401 | SH |
| 5 | GROUPON INC | GRPN | 399473206 | $15.8M | 2.60% | 657,144 | SH |
| 6 | READY CAPITAL CORP | RC | 75574U101 | $7.6M | 1.25% | 4,319,933 | SH |
| 7 | JELD-WEN HOLDING INC | JELD | 47580P103 | $4.7M | 0.77% | 3,109,621 | SH |
| 8 | CONTEXTLOGIC HOLDINGS INC | LOGC | 21078F109 | $2.6M | 0.43% | 291,341 | SH |
| 9 | SIGNATURE BANK | — | 82669G104 | $180.0K | 0.03% | 400,000 | SH |
| Period | Filed | AUM | Holdings | Accession |
|---|---|---|---|---|
| 2026-06-30 | 2026-08-14 | $607.0M | 9 | 0001104659-26-097052 |
| 2026-03-31 | 2026-05-15 | $612.9M | 7 | 0001104659-26-062410 |
| 2025-12-31 | 2026-02-17 | $561.6M | 9 | 0001104659-26-016335 |
| 2025-09-30 | 2025-11-14 | $491.4M | 6 | 0001104659-25-111862 |
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