Amentum Holdings, Inc.
Amentum Holdings, Inc. (AMTM) Stock Ownership
Institutional vs insider vs public ownership from 13F and float data — top holders, activity, and insider trades below.
SEC 13F · FMP · AMTM · as of Sep 30, 2025
Ownership Breakdown
480
Institutional Holders
▼ 1 vs Q2
$4.64B
Total Inst. Value
▼ $94.42M vs Q2
244.09M
Shares Outstanding
freeFloat 80.64%
193.63M
13F Shares Held
▼ 6.75M vs Q2
Institutional ownership = 13F shares ÷ total outstanding. Insider % = 100 − free float. Public % = free float − institution %. Data: FMP /symbol-positions-summary + /shares-float + SEC EDGAR.
Top Institutional Holders
AMTM largest shareholders · institutional ownership
Q3 2025 · SEC 13F
Showing top 10 holders
| Holder | Shares | % Owned | Weight | Value | Reported | Change |
|---|---|---|---|---|---|---|
AMERICAN SECURITIES LLC services-business services, nec | 45.03M | 18.53% | 18.53% | $1.08T | Nov 7, 2025 | — held |
INVESCO LTD. services-business services, nec | 22.12M | 9.10% | 9.10% | $529.70B | Nov 13, 2025 | ▲ 2.54M |
BLACKROCK, INC. services-business services, nec | 17.99M | 7.40% | 7.40% | $430.87B | Nov 12, 2025 | ▼ 1.00M |
VANGUARD GROUP INC services-business services, nec | 15.55M | 6.40% | 6.40% | $372.53B | Nov 7, 2025 | ▼ 979.1K |
PRIMECAP MANAGEMENT CO/CA/ services-business services, nec | 11.92M | 4.90% | 4.90% | $285.45B | Nov 12, 2025 | ▼ 112.1K |
STATE STREET CORP services-business services, nec | 6.83M | 2.81% | 2.81% | $163.66B | Nov 14, 2025 | ▼ 244.9K |
FMR LLC services-business services, nec | 6.24M | 2.57% | 2.57% | $149.33B | Nov 13, 2025 | ▲ 1.66M |
FRONTIER CAPITAL MANAGEMENT CO LLC services-business services, nec | 5.20M | 2.14% | 2.14% | $124.60B | Nov 14, 2025 | ▼ 258.1K |
KOVITZ INVESTMENT GROUP PARTNERS, LLC services-business services, nec | 3.01M | 1.24% | 1.24% | $72.04B | Nov 10, 2025 | ▲ 7.1K |
THOMPSON SIEGEL & WALMSLEY LLC services-business services, nec | 2.73M | 1.12% | 1.12% | $65.39B | Nov 12, 2025 | ▼ 56.6K |
Data from SEC Form 13F filings. Ownership bar normalised to largest holder. Change flags: isNew / isSoldOut / changeInSharesNumber (FMP extract-analytics/holder).
Institutional Activity
Q3 2025 vs prior quarter
Q3 2025
21
Increased
+9.78M shares1
New Positions
first time holders26
Decreased
−13.34M shares0
Sold Out
fully exitedNet shares change (top 50)
3.56M
+9.78M / −13.34M
Net new holders
-4
1 new / 0 exited
Based on top 50 institutional holders by position size. Fields: isNew, isSoldOut, changeInSharesNumber (FMP extract-analytics/holder, limit=50).
Insider Buying vs Selling
AMTM insider trading · insider activity
Source: SEC Form 4
5
Buy transactions
10
Sell transactions
0.50
Buy/Sell ratio
$0M
Total disposed
Recent Insider Transactions
Showing 10 most recent · Common Stock only
| Name · Role | Date | Type | Shares | Price | Value | After Trans. | Filing |
|---|---|---|---|---|---|---|---|
Heller John E. Chief Executive Officer | May 6, 2026 | Tax Withhold | 8,184 | $24.89 | $203.7K | 376.0K | Form 4 ↗ |
Mullen Sean Thomas Chief Growth Officer | May 6, 2026 | Tax Withhold | 2,762 | $24.89 | $68.7K | 32.4K | Form 4 ↗ |
Johnson Travis Barton Chief Financial Officer | May 6, 2026 | Tax Withhold | 4,097 | $24.89 | $102.0K | 118.2K | Form 4 ↗ |
Bruning Jill L Chief Technology Officer | May 6, 2026 | Tax Withhold | 2,731 | $24.89 | $68.0K | 197.5K | Form 4 ↗ |
Arnette Stephen A Chief Operating Officer | May 6, 2026 | Tax Withhold | 3,314 | $24.89 | $82.5K | 106.7K | Form 4 ↗ |
Bruning Jill L Chief Technology Officer | Mar 4, 2026 | Gift | 30,000 | — | — | 191.0K | Form 4 ↗ |
Arnette Stephen A Chief Operating Officer | Mar 2, 2026 | Tax Withhold | 750 | $30.70 | $23.0K | 96.4K | Form 4 ↗ |
Source: /insider-trading/search (FMP stable). Buy/Sell direction: acquisitionOrDisposition A=Buy, D=Sell. RSU vesting (M-Exempt) excluded from sentiment bar. All data from SEC EDGAR public filings.
About institutional & insider ownership
Amentum Holdings, Inc. (AMTM) is primarily owned by institutional investors, who hold approximately 79.3% of total shares outstanding. Company insiders own approximately 19.36%, while retail and public investors account for the remaining 1.31%.
The largest institutional shareholder of Amentum Holdings, Inc. is AMERICAN SECURITIES LLC, holding approximately 45.03 million shares — equal to 18.53% of outstanding shares — as of September 30, 2025.
A total of 480 institutional investors currently hold AMTM stock, with a combined institutional value of approximately $4.64 billion as of the most recent 13F filing period.
Frequently asked questions
AMTM ownershipAmentum Holdings, Inc. (AMTM) is primarily owned by institutional investors, who hold approximately 79.3% of shares. The largest shareholder is AMERICAN SECURITIES LLC with a 18.53% stake. Company insiders hold 19.36%. Data sourced from SEC Form 13F as of September 30, 2025.