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Livermore
Livermore
ZHEN

Mason Capital Management LLC

SEC CIK
0001218735
Latest filing
Aug 14, 2026

The latest 13F from Mason Capital Management LLC covers Q2 2026 (filed Aug 14, 2026): 9 long positions worth $607.0M. The top 10 holdings make up 100.0% of the portfolio, and the largest is ATS Corp (ATS) at 77.8%. Livermore has 22 filings on Form 13F from this institution, going back to Q1 2021.

What changed in Q2 2026

Share counts compared with Q1 2026: how many positions were new, added to, reduced or sold out, and the biggest buys and sells. Dollar amounts are estimated at the quarter-end prices implied by the filing.

Full comparison
New
2
Est. +$18.4M
Added
2
Est. +$9.00M
Reduced
1
Est. −$59.8M
Sold out
0

Top 5 holdings

Share of this quarter's portfolio value

  1. ATSATS Corp
    77.8%$472.1MHistory
  2. BKDBrookdale Senior Living Inc.
    6.8%$41.4MHistory
  3. NVRIEnviri Corp
    6.4%$38.9MHistory
  4. CCOClear Channel Outdoor Holdings, Inc.
    3.9%$23.8MHistory
  5. GRPNGroupon, Inc.
    2.6%$15.8MHistory

Biggest buys

New and added positions, by estimated amount bought

  1. GRPNGroupon, Inc.
    +$15.8MNewHistory
  2. BKDBrookdale Senior Living Inc.
    +$5.50MAddedHistory
  3. JELDJELD-WEN Holding, Inc.
    +$3.50MAddedHistory
  4. LOGCContextLogic Holdings Inc.
    +$2.59MNewHistory

Largest weight increases

New and added positions, by percentage points of the portfolio gained

  1. GRPNGroupon, Inc.
    +2.60 pp0.0% → 2.6%History
  2. BKDBrookdale Senior Living Inc.
    +1.84 pp5.0% → 6.8%History
  3. JELDJELD-WEN Holding, Inc.
    +0.61 pp0.2% → 0.8%History
  4. LOGCContextLogic Holdings Inc.
    +0.43 pp0.0% → 0.4%History

Biggest sells

Reduced and sold-out positions, by estimated amount sold

  1. NVRIEnviri Corp
    −$59.8MReducedHistory

Largest weight decreases

Reduced and sold-out positions, by percentage points of the portfolio lost

  1. NVRIEnviri Corp
    −7.99 pp14.4% → 6.4%History

Metrics

13F metrics for Q2 2026, computed only from the numbers in the filings. Definitions below.

Portfolio value
$607.0M
−$5.83M (−1.0%) vs. prior quarter
Positions
9
+2 vs. prior quarter
Top 10 concentration
100.0%
Top 10 as share of value
Turnover
4.5%
Q2 2026, one quarter
Average holding period
11.5 quarters
Weighted by value

How these are calculated

  • Portfolio value: the market value of all long positions in the 13F, as reported at quarter end, excluding options.
  • Top 10 concentration: the combined value of the 10 largest positions as a share of portfolio value.
  • Turnover: the smaller of this quarter's estimated purchases and estimated sales, divided by the average of this and last quarter's portfolio value. Estimates multiply the change in shares by the quarter-end price implied by the filing (market value divided by shares); new positions use this quarter's value and sold-out positions last quarter's. Only positions reported in shares count, and it is not calculated when the previous quarter was not filed.
  • Average holding period: how many consecutive quarters each current position has been held (including this one; a quarter without the position or without a filing starts the count over), weighted by this quarter's value. Counting starts with the first 13F in Livermore (Q1 2021), so positions held before then are understated.

13F filings by quarter

22 quarters, going back to Q1 2021. Bars show each quarter's 13F portfolio value; quarters without a filing are left blank.

Peak $1.16B (Q3 2023)

Q1 2021: $268.0MQ2 2021: $450.1MQ3 2021: $215.8MQ4 2021: $208.9MQ1 2022: $313.3MQ2 2022: $281.4MQ3 2022: $257.8MQ4 2022: $231.1MQ1 2023: $234.2MQ2 2023: $1.03BQ3 2023: $1.16BQ4 2023: $893.9MQ1 2024: $727.8MQ2 2024: $538.2MQ3 2024: $502.6MQ4 2024: $470.5MQ1 2025: $427.2MQ2 2025: $511.5MQ3 2025: $491.4MQ4 2025: $561.6MQ1 2026: $612.9MQ2 2026: $607.0M
Q1 2021Q2 2026
13F filings of Mason Capital Management LLC by quarter
QuarterFiledPositionsValueTop 3 holdingsChangesFiling
Q2 2026Aug 14, 20269$607.0MATSBKDNVRIvs. Q1 2026SEC
Q1 2026May 15, 20267$612.9MATSNVRIBKDvs. Q4 2025SEC
Q4 2025Feb 17, 20269$561.6MATSBKDSOLSvs. Q3 2025SEC
Q3 2025Nov 14, 20256$491.4MATSKVUEBKDvs. Q2 2025SEC
Q2 2025Aug 14, 20254$511.5MATSCCOCohen Circle Acquisition Corvs. Q1 2025SEC
Q1 2025May 15, 20255$427.2MATSParamount GlobalCCOvs. Q4 2024SEC
Q4 2024Feb 14, 20254$470.5MATSCCORCvs. Q3 2024SEC
Q3 2024Nov 14, 20246$502.6MATSMDRXBarnes Group Incvs. Q2 2024SEC
Q2 2024Aug 14, 20246$538.2MATSBarnes Group IncCCOvs. Q1 2024SEC
Q1 2024May 15, 20246$727.8MATSBarnes Group IncSDRLvs. Q4 2023SEC
Q4 2023Feb 15, 20247$893.9MATSState Street Industrial Select Sector SPDR ETFBarnes Group Incvs. Q3 2023SEC
Q3 2023Nov 14, 20238$1.16BATSATVIVMWvs. Q2 2023SEC
Q2 2023Aug 14, 202310$1.03BATSVMWATVIvs. Q1 2023SEC
Q1 2023May 15, 202312$234.2MGEOWFRDState Street Industrial Select Sector SPDR ETFvs. Q4 2022SEC
Q4 2022Feb 14, 202312$231.1MWFRDGEOMSGSvs. Q3 2022SEC
Q3 2022Nov 14, 202212$257.8MTWTRWFRDGEOvs. Q2 2022SEC
Q2 2022Aug 15, 202216$281.4MCXWGEOASTLvs. Q1 2022SEC
Q1 2022May 16, 202216$313.3MCCOCXWVVVvs. Q4 2021SEC
Q4 2021Feb 14, 20227$208.9MCCOCXWASTLvs. Q3 2021SEC
Q3 2021Nov 15, 202132$215.8MCCOCXWLegato Merger Corp.vs. Q2 2021SEC
Q2 2021Aug 16, 202131$450.1MHLFGLDCCOvs. Q1 2021SEC
Q1 2021May 17, 202123$268.0MHLFCCOInvesco Exchange Traded FD T–SEC

13D and 13G filings

Companies where Mason Capital Management LLC reports owning 5% or more on Schedule 13D or 13G, and its latest filings.

Current stakes of 5% or more

2 companies, largest stake first.

Companies where Mason Capital Management LLC owns 5% or more
CompanyLatest formStakeChangeFirst filedLatest filingFiling
MDRXVeradigm Inc.13G5.80%6.28M sharesNewJan 29, 20261 filingJan 29, 2026SEC
JELDJELD-WEN Holding, Inc.13G5.50%4.79M sharesNewAug 5, 20261 filingAug 5, 2026SEC

Latest filings

15 filings on file made by Mason Capital Management LLC or listing it as a reporting person, newest first.

Schedule 13D and 13G filings by Mason Capital Management LLC
CompanyFiled (ET)FormStakeChangeEvent dateFiling
NVRIEnviri CorpAug 14, 20261:30 PM ET13G/A0.00%0 shares−5.50 ppfrom 5.50%Below 5%Jun 30, 2026SEC
JELDJELD-WEN Holding, Inc.Aug 5, 20265:13 PM ET13G5.50%4.79M sharesNewJul 29, 2026SEC
NVRIEnviri CorpJul 14, 20264:30 PM ET13G3.70%1.03M sharesNewBelow 5%Jun 1, 2026SEC
NVRIEnviri CorpApr 6, 20265:40 PM ET13G5.50%4.51M sharesNewMar 30, 2026SEC
MDRXVeradigm Inc.Jan 29, 20264:10 PM ET13G5.80%6.28M sharesNewJan 22, 2026SEC
ATSATS CorpNov 13, 202413G/AOld format–––SEC
ATSATS CorpFeb 14, 202413GOld format–New–SEC
PSQHPSQ Holdings, Inc.Jul 21, 202313D/AOld format–––SEC
PSQHPSQ Holdings, Inc.Jul 19, 202313D/AOld format–––SEC
PSQHPSQ Holdings, Inc.Jun 26, 202313DOld format–New–SEC
CCOClear Channel Outdoor Holdings, Inc.Feb 14, 202213G/AOld format–––SEC
CXWCoreCivic, Inc.Jan 5, 202213D/AOld format–––SEC
CXWCoreCivic, Inc.Nov 12, 202113DOld format–New–SEC
Legato Merger Corp.Aug 16, 202113GOld format–New–SEC
CCOClear Channel Outdoor Holdings, Inc.Feb 9, 202113G/AOld format–––SEC