Mason Capital Management LLC holds a concentrated book of 7 stocks worth $612.9M as of Q1 2026 (disclosed May 15, 2026, a ~45-day 13F lag). This quarter they opened Enviri Corp and trimmed Brookdale Senior Living Inc. Their largest long position is Ats Corp at 75% of the equity book.
The public view is the crawlable proof. The same sourced dataset is available through REST and MCP for agents, research scripts, and back-office tools.
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.
Top-heavy: concentrated book
Share of the disclosed book in its largest positions. A higher top-5 share means a more concentrated, higher-conviction portfolio.
100% 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, no cost basis
Bars show each stock's share of the portfolio. Click a row for its position history.
| # | Security | Value | Shares | % Port | Last move | History |
|---|---|---|---|---|---|---|
| 1 | Ats Corporation COM | $462.6M | 16.40M | 75.5% | ▲+5.4% Added · +841K sh | |
| 2 | Enviri Corp COM | $88.2M | 4.49M | 14.4% | ▲New New position | |
| 3 | Brookdale Senior Living Inc COM | $30.6M | 2.23M | 5.0% | ▼−38% Reduced · −1.4M sh | |
| 4 | Clear Channel Outdoor Hldgs COM | $23.3M | 9.83M | 3.8% | —Held | |
| 5 | Ready Capital Corp REIT | $7.0M | 4.32M | 1.1% | ▲+14% Added · +544K sh | |
| 6 | Jeld-Wen Holding Inc COM | $963K | 776.9K | 0.2% | ▲New New position | |
| 7 | Signature Bank COM | $260K | 400.0K | 0.0% | —Held |
As-of date vs the date the SEC received each filing
Holdings from SEC EDGAR 13F-HR filings, updated quarterly ~45 days after quarter-end. Public domain. The book and weighting are long equity only; disclosed put/call options are listed separately and excluded from those totals. Price-derived performance is withheld until the price-source policy and freshness gate are green.