Mason Capital Management LLC holds a concentrated book of 9 reported positions worth $607.0M as of Q2 2026 (disclosed Aug 14, 2026, a ~45-day 13F lag). This quarter they opened Groupon Inc and trimmed Enviri Corp. Their largest long position is Ats Corp at 78% of the reported non-option book. Cloning the disclosed picks since 2025 would be -19% (-17.4%/yr). That is a simulation of the disclosed long book, not audited returns.
Following at the filing date actually beat the quarter-end book by 13.3 points over this window.
Growth of $10,000 cloning Mason Capital Management LLC's disclosed long 13F book, rebalanced on each filing date (so it reflects each quarter's actual reporting lag, ~45 days for the latest filing, with no look-ahead), total-return basis (dividends reinvested), derived from end-of-day prices. “Their reported book” values the same picks from quarter-end, before they were public. S&P 500 is SPY total return over the same window. Excludes shorts, cash, options and non-13F holdings. Not investment advice.
Top-heavy: concentrated book
Excluding Ats Corp (78% of the book), the rest is a concentrated book:
Share of the disclosed book in its largest positions. A higher top-5 share means a more concentrated, higher-conviction portfolio.
94% mapped to company sectors
Direct operating-company sectors from our SIC-based security master. ETF/fund and unclassified holdings stay visible separately; this is not ETF look-through exposure.
Estimated $ traded · quarter-end prices (an exit at the prior quarter-end), no cost basis
Other tracked managers holding the same core names as Mason Capital Management LLC
| Manager / fund | Shared names | Their $ in those |
|---|---|---|
| Turtle Creek Asset Management Inc. | 2 / 9 | $158.7M |
| Nexpoint Asset Management, L.P. | 2 / 9 | $27.2M |
| Varcov Co. | 2 / 9 | $1.9M |
| Quinn Opportunity Partners LLC | 4 / 9 | $12.2M |
| CenterBook Partners LP | 3 / 9 | $11.4M |
| Bayforest Capital Ltd | 2 / 9 | $493K |
| Diametric Capital, LP | 2 / 9 | $3.6M |
| Prelude Capital Management, LLC | 2 / 9 | $4.8M |
Ranked by the share of each fund's own book sitting in the names it shares with Mason Capital Management LLC: only funds sharing at least a tenth of the book qualify. Index giants, bank custody books and market makers are excluded. They hold everything, so their overlap says nothing.
Bars show each position's share of the portfolio. Click a row for its position history.
| # | Security | Value | Shares | % Port | Last move | History |
|---|---|---|---|---|---|---|
| 1 | Ats Corporation COM | $472.1M | 16.40M | 77.8% | —Held | |
| 2 | Brookdale Senior Living Inc COM | $41.4M | 2.58M | 6.8% | ▲+15% Added · +342K sh | |
| 3 | Enviri Corp COM | $38.9M | 1.77M | 6.4% | ▼−61% Reduced · −2.7M sh | |
| 4 | Clear Channel Outdoor Hldgs COM | $23.8M | 9.83M | 3.9% | —Held | |
| 5 | Groupon Inc COM | $15.8M | 657.1K | 2.6% | ▲New New position | |
| 6 | Ready Capital Corp REIT | $7.6M | 4.32M | 1.2% | —Held | |
| 7 | Jeld-Wen Holding Inc COM | $4.7M | 3.11M | 0.8% | ▲+300% Added · +2.3M sh | |
| 8 | Contextlogic Holdings Inc COM | $2.6M | 291.3K | 0.4% | ▲New New position | |
| 9 | Signature Bank COM | $180K | 400.0K | <0.1% | —Held |
This fund page is the Follow view. The Build view lets your agent pull holdings, quarter changes, overlap, and source filings through API or MCP.
curl -H "Authorization: Bearer YOUR_API_KEY" \ "https://arkolith.com/api/v1/funds/1218735/holdings"
Use Arkolith to show MASON CAPITAL MANAGEMENT LLC's latest holdings, largest changes, and filing provenance.
As-of date vs the date the SEC received each filing
Reported 13F total per quarter. Raw filing totals can include option notional.
Holdings from SEC EDGAR 13F-HR filings, updated quarterly, filed up to 45 days after quarter-end. Public domain. Book totals and portfolio weights cover reported non-option positions, which can include notes and warrants. Disclosed put/call options are listed separately and excluded from those totals. The performance line is a simulation of the disclosed long book, not an audited return.