WESTFIELD CAPITAL MANAGEMENT CO LP
Q1 2026 Form 13-F

BOSTON, MASSACHUSETTS
CIK 0001177719 · CRD 146990 · SEC-registered investment adviser
$23.8B Reported Value Total

WESTFIELD CAPITAL MANAGEMENT COMPANY, L.P. reports 1,118 total accounts under management (AUM). There are 1,118 discretionary accounts valued at $24,404,194,926, and 0 non-discretionary accounts.

Source: Form ADV filed * Note that certain holdings are exempt from Form 13-F reporting, so the AUM totals may be greater than the Form 13-F total.
SEC Registered Discretionary Manager
Firm Brochure (Part 2A) Client Relationship Summary (Form CRS)
Private funds (Form ADV)
11 funds · $185.4M gross asset value
Other: $68.8M · Hedge Fund: $34.8M · Private Equity Fund: $128.8K
Source: Form ADV filed 2026-07-01
Reported value
$23.8B
Quarter over quarter
-1.5%
Holdings
250
Top-10 concentration
30.3%

Filing Structure

Reports holdings for

Holdings reported by

Key People

Form ADV owners & control persons
William Albert Muggia
MEMBER OF MANAGEMENT COMMITTEE
Kathryn Ann Kearney
PARTNER, CHIEF FINANCIAL OFFICER AND CHIEF COMPLIANCE OFFICER
Richard Dailyong Lee
CHIEF INVESTMENT OFFICER
Q4 2025
Q2 2026
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Coverage begins with the second quarter of 2013. Earlier quarters are not shown while their accuracy is being verified.

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Q1 2026 13F filing summary

Period of report March 31, 2026
Filed May 11, 2026
Form 13F-HR
Reported value $23.8B
Positions 250
Change in reported value -0.7%
New positions 46
Exited positions 37
Position turnover 28.9%
Top-10 concentration 30.3%

13F filings by quarter

Quarter Positions Value
Q2 2026 13F
Filed Aug 12, 2026
 278 $30.6B
Q1 2026 13F
Filed May 11, 2026
 250 $23.8B
Q4 2025 13F
Filed Feb 11, 2026
 241 $24.0B
Q3 2025 13F
Filed Nov 12, 2025
 235 $23.8B
Q2 2025 13F
Filed Aug 12, 2025
 239 $23.8B
Q1 2025 13F
Filed May 9, 2025
 244 $20.5B
Q4 2024 13F
Filed Feb 11, 2025
 239 $23.0B
Q3 2024 13F
Filed Nov 12, 2024
 247 $22.1B
Q2 2024 13F
Filed Aug 14, 2024
 248 $20.4B
Q1 2024 13F
Filed May 10, 2024
 244 $19.0B
Q4 2023 13F
Filed Feb 9, 2024
 239 $17.2B
Q3 2023 13F
Filed Nov 13, 2023
 234 $14.7B
Q2 2023 13F
Filed Aug 11, 2023
 227 $15.7B
Q1 2023 13F
Filed May 12, 2023
 222 $14.2B
Q4 2022 13F
Filed Feb 13, 2023
 226 $13.0B
Q3 2022 13F
Filed Nov 14, 2022
 230 $12.6B
Q2 2022 13F
Filed Aug 12, 2022
 235 $12.7B
Q1 2022 13F
Filed May 16, 2022
 235 $15.6B
Q4 2021 13F
Filed Feb 10, 2022
 244 $16.8B
Q3 2021 13F
Filed Nov 12, 2021
 235 $16.6B

33 earlier quarters on file — choose one from the quarter menu above.

Top 20 holdings · Q1 2026

# Holding Reported value % of portfolio
1 NVDA NVIDIA CORPORATION $1.1B 4.62%
2 ASND ASCENDIS PHARMA A/S $1.1B 4.62%
3 FIX COMFORT SYS USA INC $856.2M 3.59%
4 AAPL APPLE INC $795.2M 3.34%
5 FTAI FTAI AVIATION LTD $697.8M 2.93%
6 MSFT MICROSOFT CORP $610.6M 2.56%
7 GOOGL ALPHABET INC $582.8M 2.45%
8 HWM HOWMET AEROSPACE INC $527.7M 2.21%
9 VRT VERTIV HOLDINGS CO $481.5M 2.02%
10 AMZN AMAZON COM INC $474.8M 1.99%
11 AXON AXON ENTERPRISE INC $451.9M 1.9%
12 AVGO BROADCOM INC $382.8M 1.61%
13 LLY ELI LILLY & CO $335.3M 1.41%
14 TPR TAPESTRY INC $310.3M 1.3%
15 META META PLATFORMS INC $301.4M 1.26%
16 LPLA LPL FINL HLDGS INC $265.2M 1.11%
17 MKSI MKS INC. $240.6M 1.01%
18 INSM INSMED INC $240.1M 1.01%
19 PCVX VAXCYTE INC $211.9M 0.89%
20 RKLB ROCKET LAB CORP $203.7M 0.85%

Values as reported on the Q1 2026 Form 13F. Every position is in the holdings table below.

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