WESTFIELD CAPITAL MANAGEMENT CO LP

Long Only Manager

WESTFIELD CAPITAL MANAGEMENT CO LP is a Long Only Manager based in Boston, MA led by William Albert Muggia, managing $23.8B across 235 long positions as of Q3 2025 with 32% Technology concentration.

CEOWilliam Albert Muggia

Portfolio Value: $23.8B
Positions: 235
Top Holding: NVDA at 5.09%
Last Reported: Q3 2025

AddressOne Financial Center, Boston, MA, 02111, United States

Top Holdings

Largest long holdings in WESTFIELD CAPITAL MANAGEMENT CO LP's portfolio (30.5% of total portfolio)

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Holding	Sector	Position	Weight	Traded	Ownership	Owned Since
1 Nvidia NVDA	Semiconductors Technology	$1.2B	5.09%	-$193.7M Sold	0.03% 6.5M shares	Q4 2019 Held for 5y 11m
2 ASND Ascendis Pharma ASND	Unknown Unknown	$1.0B	4.39%	-$38.1M Sold	— 5.3M shares	Q4 2022 Held for 2y 11m
3 Microsoft MSFT	Software - Infrastructure Technology	$883.2M	3.71%	-$27.0M Sold	0.02% 1.7M shares	≤ Q2 2013 Held for 12y 5m+
4 Apple AAPL	Consumer Electronics Technology	$849.1M	3.56%	-$40.6M Sold	0.02% 3.3M shares	≤ Q2 2013 Held for 12y 5m+
5 Comfort Systems USA FIX	Engineering & Construction Industrials	$687.5M	2.88%	-$85.2M Sold	2.36% 833.2K shares	Q4 2023 Held for 1y 11m
6 Meta Platforms, Inc. META	Internet Content & Information Communication Services	$563.8M	2.37%	-$66.6M Sold	0.03% 767.7K shares	Q3 2013 Held for 12y 2m
7 Amazon AMZN	Specialty Retail Consumer Cyclical	$558.1M	2.34%	-$122.7M Sold	0.02% 2.5M shares	Q3 2015 Held for 10y 2m
8 Alphabet Inc. GOOGL	Internet Content & Information Communication Services	$545.7M	2.29%	-$79.5M Sold	0.02% 2.2M shares	≤ Q2 2013 Held for 12y 5m+
9 Axon Enterprise, Inc. AXON	Aerospace & Defense Industrials	$523.3M	2.20%	-$43.7M Sold	0.93% 729.2K shares	Q4 2022 Held for 2y 11m
10 Howmet Aerospace HWM	Industrial - Machinery Industrials	$393.9M	1.65%	+$18.0M Bought	0.50% 2.0M shares	Q1 2025 Held for 8 months

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Changes

Portfolio activity, position movements, and quarter-over-quarter changes in WESTFIELD CAPITAL MANAGEMENT CO LP's latest filing

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Market Value

$23.8B

Prior: $23.8B

Q/Q Change

-0.046%

-$10.9M

Net Flows % of MV

-11.5%

Turnover Ratio

17.33%

New Purchases

16 stocks

$856.6M

Added To

80 stocks

+$1.4B

Sold Out Of

47 stocks

$2.2B

Reduced Holdings

99 stocks

-$2.9B

Increased Positions

Position	Shares Δ	Change
1 Bloom Energy BE	New	0 → 1.7M +$141.7M
2 Karman Holdings Inc. KRMN	New	0 → 1.4M +$102.9M
3 Kratos Defense & Security Solutions KTOS	New	0 → 1.0M +$91.9M
4 ADMA Biologics ADMA	New	0 → 5.1M +$74.9M
5 C.H. Robinson Worldwide CHRW	New	0 → 550.8K +$72.9M

Decreased Positions

Position	Shares Δ	Change
1 Salesforce CRM	Sold	647.5K → 0 −$176.6M
2 Badger Meter BMI	Sold	612.8K → 0 −$150.1M
3 Texas Roadhouse TXRH	Sold	705.6K → 0 −$132.2M
4 Applied Materials AMAT	Sold	694.4K → 0 −$127.1M
5 Lantheus Holdings LNTH	Sold	1.5M → 0 −$122.4M