MASON CAPITAL MANAGEMENT LLC: ATS (ATS): Quarterly 13F Position History
As of Q1 2026, MASON CAPITAL MANAGEMENT LLC reported 16,404,170 shares of ATS (ATS), worth $462.6M and representing 75.5% of its 13F equity book. Quarter-over-quarter share count change: + 840,602 (+5.4%) . The position first appeared in Q2 2023 and has been disclosed across 12 13F-HR filings in Pactolio's tracked window.
- 16,404,170Shares Held (Latest Filing)
- $462.6MReported Market Value (Latest Filing)
- 75.5%Portfolio Weight (% of 13F Equity Book)
- +840,602Quarter-over-Quarter Share Change
- +$34.0MQuarter-over-Quarter Value Change
- 17,849,765Peak Reported Shares (Historical)
Quarterly 13F-HR Disclosure History Source: SEC 13F-HR filings, 12 quarter s
| Quarter | Shares | QoQ Share Change | Share Change (%) | Market Value | Weight | Implied Price |
|---|---|---|---|---|---|---|
| Q1 2026 | 16,404,170 | +840,602 | +5.4% | $462.6M | 75.5% | $28.2 |
| Q4 2025 | 15,563,568 | 0 | — | $428.6M | 76.3% | $27.5 |
| Q3 2025 | 15,563,568 | 0 | — | $407.8M | 83.0% | $26.2 |
| Q2 2025 | 15,563,568 | 0 | — | $496.2M | 97.0% | $31.9 |
| Q1 2025 | 15,563,568 | +648,803 | +4.4% | $388.0M | 90.8% | $24.9 |
| Q4 2024 | 14,914,765 | 0 | — | $454.6M | 96.6% | $30.5 |
| Q3 2024 | 14,914,765 | +565,000 | +3.9% | $433.3M | 86.2% | $29.1 |
| Q2 2024 | 14,349,765 | 0 | — | $463.6M | 86.1% | $32.3 |
| Q1 2024 | 14,349,765 | 3,500,000 | -19.6% | $654.1M | 89.9% | $45.6 |
| Q4 2023 | 17,849,765 | 0 | — | $768.8M | 86.0% | $43.1 |
| Q3 2023 | 17,849,765 | 0 | — | $760.8M | 65.4% | $42.6 |
| Q2 2023 | 17,849,765 | — | — | $822.7M | 80.2% | $46.1 |
Methodology & FAQ
How This Position History Is Sourced
Each row is one SEC Form 13F-HR filing disclosing this position. Share count, market value, and reported quarter are taken verbatim from the filing; portfolio weight is recomputed against the same filing's total reported equity book. Implied price-per-share is market value divided by shares — a quarter-end mark, not the manager's cost basis. See the full methodology document for the normalization rules.
When did MASON CAPITAL MANAGEMENT LLC first disclose a ATS position in 13F-HR filings?
MASON CAPITAL MANAGEMENT LLC first reported ATS (ATS) on its 13F-HR filing for the period ending 2023-06-30 (Q2 2023). The position has appeared on 12 reported quarters within Pactolio's tracked window.
What was MASON CAPITAL MANAGEMENT LLC's most recent quarter-over-quarter share-count change in ATS?
Between Q4 2025 and Q1 2026, MASON CAPITAL MANAGEMENT LLC added 840,602 shares of ATS (+5.4%), bringing the total reported position to 16,404,170 shares at a market value of $462.6M.
Does the implied price-per-share represent MASON CAPITAL MANAGEMENT LLC's cost basis in ATS?
No. The implied price-per-share column is the 13F-HR reported market value divided by reported share count on the filing date (end of quarter). It is a quarter-end mark, not a cost basis or transaction price. Use it as a sanity check on the value column, not as an indicator of the manager's entry or exit price.