DOSSIER · 13F-HR · Q1 2026

MASON CAPITAL MANAGEMENT LLC

MASON's asset manager based in Boston, MA $613M in tracked AUM across 7 positions as of Q1 2026.

M
MASON·Boston, MA·Asset Manager
CIK 0001218735 · last filed Mar 31, 2026
Total AUM
$613M
17.0%
vs prior
Holdings
7
positions
Whale Score
75
75
strong
Activity
no data
changes this Q
Top sector
Tech
6% weight
concentration
AI Analysis · Q1 2026 · Q1 2026
Comprehensive Analysis of Mason Capital Management LLC 13F Filing
1. Portfolio Overview

Mason Capital Management LLC exhibits a highly concentrated investment strategy with this 13F filing for the period ending September 30, 2025. The firm manages a total portfolio value of approximately $470.38 million, spread across just five holdings. This represents a decrease of 8.0% from the previous quarter's value of $511.53 million. The reduction in portfolio value is likely attributable to market...

Quarter at a glance — Q1 2026

Position-change comparison pending.

No quarter-over-quarter changes available.

Top 10 holdings

By portfolio weight as of Q1 2026.

#HoldingValueSharesWeight
01
ATS
ATS CORPORATION
$463M16.4M75.5%
02
NVRI
ENVIRI CORP
$88M4.5M14.4%
03
BKD
BROOKDALE SENIOR LIVING INC
$31M2.2M5.0%
04
CCO
CLEAR CHANNEL OUTDOOR HLDGS
$23M9.8M3.8%
05
RC
READY CAPITAL CORP
$7M4.3M1.1%
06
JELD
JELD-WEN HOLDING INC
$963,337777K0.2%
07
SBNY
SIGNATURE BANK
$260,000400K0.0%

Filing history

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