Thompson Siegel & Walmsley’s Amentum Holdings AMTM Stock Holding History

Thompson Siegel & Walmsley’s Portfolio AMTM Stock Details AMTM Fund Activity

Bought

Maintained

Sold

Quarter	Market Value	Status	Shares	Change in Stake	Trade Value	Portfolio Weight	Portfolio Position
2026 Q2	$47.2M	Buy	2,281,945 +756,061	+50%	+$18.3M	0.85%	37
2026 Q1	$39.8M	Sell	1,525,884 -395,925	-21%	-$12.4M	0.7%	55
2025 Q4	$55.7M	Sell	1,921,809 -808,489	-30%	-$20.7M	0.94%	31
2025 Q3	$65.4M	Sell	2,730,298 -56,615	-2%	-$1.38M	1.06%	26
2025 Q2	$65.8M	Sell	2,786,913 -539,465	-16%	-$11.3M	1.09%	23
2025 Q1	$60.5M	Buy	3,326,378 +1,377,694	+71%	+$28.1M	1.02%	38
2024 Q4	$41M	Buy	1,948,684 +1,606,442	+469%	+$41.5M	0.64%	62
2024 Q3	$11M	Buy	+342,242	New	+$9.75M	0.16%	126

Other funds holding AMTM

American Securities New York $3.75B AUM 23.12% 1-Year Est. Return

Invesco Atlanta, Georgia $1.26T AUM 61.52% 1-Year Est. Return

BlackRock New York $6.73T AUM 46.02% 1-Year Est. Return

Primecap Management Pasadena, California $169B AUM 114.72% 1-Year Est. Return

Vanguard Portfolio Management Malvern, Pennsylvania $2.22T AUM

Vanguard Capital Management Malvern, Pennsylvania $4.68T AUM

Fidelity Investments Boston, Massachusetts $2.3T AUM 54.33% 1-Year Est. Return

Dimensional Fund Advisors Austin, Texas $552B AUM 44.19% 1-Year Est. Return

State Street Boston, Massachusetts $3.37T AUM 44.26% 1-Year Est. Return

FCM

Frontier Capital Management Boston, Massachusetts $10.7B AUM 67.78% 1-Year Est. Return

Thompson Siegel & Walmsley's AMTM Position: Q2 2026 in Review

Thompson Siegel & Walmsley increased its Amentum Holdings (AMTM) stake by 50% in Q2 2026, buying an estimated $18.3M and bringing the position to 2,281,945 shares worth $47.2M. The position accounts for 0.85% of the portfolio, ranked #37.

Thompson Siegel & Walmsley first reported a position in AMTM in Q3 2024 and has held it in 8 quarters since. The position peaked at $65.8M in Q2 2025. 460 funds tracked by Wall St. Rank hold AMTM as of Q2 2026.

Thompson Siegel & Walmsley held 2,281,945 shares of Amentum Holdings worth $47.2M as of Q2 2026.
Thompson Siegel & Walmsley bought 756,061 Amentum Holdings shares in Q2 2026, an estimated $18.3M.
Amentum Holdings made up 0.85% of Thompson Siegel & Walmsley's portfolio in Q2 2026, its #37 holding.
Thompson Siegel & Walmsley first reported a position in Amentum Holdings in Q3 2024 and has held it in 8 quarters since.
Thompson Siegel & Walmsley's Amentum Holdings position peaked at $65.8M in Q2 2025.
460 funds tracked by Wall St. Rank held Amentum Holdings as of Q2 2026.

Based on Thompson Siegel & Walmsley's 13F filing for Q2 2026, filed 11 Aug 2026.