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WESTFIELD CAPITAL MANAGEMENT CO LP — 13F Holdings & Portfolio

CIK 1177719 · latest 13F-HR filed 2026-08-12

Backtest portfolio

WESTFIELD CAPITAL MANAGEMENT CO LP manages $30.61B in 13F-reported U.S. long-equity assets across 278 reported positions as of its 2026-06-30 13F-HR filing. Its largest disclosed positions are NVDA (5.28%), GOOGL (4.38%), ASND (4.18%). Quarter over quarter (versus its 2026-03-31 filing) the fund opened 69 new positions, exited 41, added to 128, and trimmed 60.

AUM is the long-equity portion reported on Form 13F-HR. Excludes short positions, cash, foreign holdings, and non-13F assets. For informational purposes only — not investment advice.

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AUM

$30.61B

Long-equity book

Holdings

278

Distinct positions

Period

2026-06-30

Filed 2026-08-12

Q/Q Activity

+69 / −41 / ↑128 / ↓60

vs 2026-03-31

Portfolio charts

Latest quarter's book, what changed, and how the portfolio has evolved across filings.

Firm Profile & Key People
Name Title / Status Ownership Type

Quarter-over-quarter changes

Share-count changes vs the prior 13F.

Top Adds (vs prior quarter)

  • ALPHABET INC$757.0M +129.9%
  • NVIDIA CORPORATION$515.0M +46.7%
  • AXON ENTERPRISE INC$384.2M +85.0%
  • SNOWFLAKE INC$333.5M +307.7%
  • ADVANCED MICRO DEVICES INC$233.1M +22828.8%
Show all 128 →

Top Trims

  • AMAZON COM INC-$269.9M -56.8%
  • NETFLIX INC.-$168.6M -89.0%
  • MARVELL TECHNOLOGY INC-$161.8M -97.6%
  • BLOOM ENERGY CORP-$158.2M -98.0%
  • COMFORT SYS USA INC-$151.8M -17.7%
Show all 60 →

New Positions

  • ASCENDIS PHARMA A/S$1.28B
  • CARPENTER TECHNOLOGY CORP$193.7M
  • PTC THERAPEUTICS INC$159.6M
  • LAM RESEARCH CORP$123.8M
  • ASML HLDG NV$114.3M
Show all 69 →

Exited Positions

  • ASCENDIS PHARMA A/S$1.10B
  • KRATOS DEFENSE & SEC SOLUTIO$110.2M
  • AMERICAN INTL GROUP INC$109.8M
  • PALANTIR TECHNOLOGIES INC$98.7M
  • GENEDX HOLDINGS CORP$87.9M
Show all 41 →
All Holdings

Rows tagged Call or Put are options positions, not stock. Per SEC Form 13F-HR, Value shows the notional value of the underlying (shares covered × underlying price), not the option premium. Shares is the number of underlying shares covered (divide by 100 for contract count).

# Issuer Symbol CUSIP Value Weight Shares Type
1 NVIDIA CORPORATION NVDA 67066G104 $1.62B 5.28% 8,079,926 SH
2 ALPHABET INC GOOGL 02079K305 $1.34B 4.38% 3,749,074 SH
3 ASCENDIS PHARMA A/S ASND K08588103 $1.28B 4.18% 4,798,267 SH
4 AXON ENTERPRISE INC AXON 05464C101 $836.1M 2.73% 1,491,490 SH
5 FTAI AVIATION LTD FTAI G3730V105 $794.6M 2.60% 2,937,228 SH
6 APPLE INC AAPL 037833100 $744.7M 2.43% 2,573,774 SH
7 COMFORT SYS USA INC FIX 199908104 $704.5M 2.30% 355,433 SH
8 BROADCOM INC AVGO 11135F101 $588.0M 1.92% 1,556,522 SH
9 MICROSOFT CORP MSFT 594918104 $527.6M 1.72% 1,414,294 SH
10 HOWMET AEROSPACE INC HWM 443201108 $516.6M 1.69% 1,921,476 SH
11 ELI LILLY & CO LLY 532457108 $499.8M 1.63% 416,732 SH
12 SNOWFLAKE INC SNOW 833445109 $441.9M 1.44% 1,736,498 SH
13 MKS INC. MKSI 55306N104 $413.0M 1.35% 928,617 SH
14 META PLATFORMS INC META 30303M102 $381.6M 1.25% 677,389 SH
15 VERTIV HOLDINGS CO VRT 92537N108 $353.0M 1.15% 1,054,361 SH
16 GE VERNOVA INC GEV 36828A101 $283.5M 0.93% 241,272 SH
17 MICRON TECHNOLOGY INC MU 595112103 $263.4M 0.86% 228,203 SH
18 VISA INC V 92826C839 $261.6M 0.85% 762,403 SH
19 API GROUP CORP APG 00187Y100 $260.6M 0.85% 6,154,301 SH
20 TAPESTRY INC TPR 876030107 $248.3M 0.81% 1,696,569 SH
21 RHYTHM PHARMACEUTICALS INC RYTM 76243J105 $245.2M 0.80% 2,208,595 SH
22 LIFE TIME GROUP HOLDINGS INC LTH 53190C102 $244.8M 0.80% 5,995,254 SH
23 TAIWAN SEMICONDUCTOR MANUFAC TSM 874039100 $244.0M 0.80% 510,999 SH
24 GUARDANT HEALTH INC GH 40131M109 $243.7M 0.80% 1,624,459 SH
25 QUANTA SVCS INC PWR 74762E102 $238.7M 0.78% 331,489 SH
26 SERVICENOW INC NOW 81762P102 $235.7M 0.77% 2,373,711 SH
27 ADVANCED MICRO DEVICES INC AMD 007903107 $234.2M 0.76% 403,081 SH
28 PALO ALTO NETWORKS INC PANW 697435105 $224.5M 0.73% 658,331 SH
29 WOODWARD INC WWD 980745103 $224.0M 0.73% 526,505 SH
30 ARISTA NETWORKS INC ANET 040413205 $223.7M 0.73% 1,317,096 SH
31 LPL FINL HLDGS INC LPLA 50212V100 $223.4M 0.73% 793,061 SH
32 ROCKET LAB CORP RKLB 773121108 $214.9M 0.70% 2,114,005 SH
33 AMER SPORTS INC AS G0260P102 $214.7M 0.70% 6,344,923 SH
34 CLOUDFLARE INC NET 18915M107 $204.9M 0.67% 835,502 SH
35 AMAZON COM INC AMZN 023135106 $204.9M 0.67% 859,806 SH
36 GARMIN LTD GRMN H2906T109 $204.5M 0.67% 861,057 SH
37 REGAL REXNORD CORPORATION RRX 758750103 $204.1M 0.67% 856,976 SH
38 NATERA INC NTRA 632307104 $197.2M 0.64% 726,628 SH
39 MORGAN STANLEY MS 617446448 $196.6M 0.64% 940,560 SH
40 CARPENTER TECHNOLOGY CORP CRS 144285103 $193.7M 0.63% 314,082 SH
41 SAMSARA INC IOT 79589L106 $189.3M 0.62% 5,836,459 SH
42 DYNATRACE INC DT 268150109 $186.6M 0.61% 4,249,229 SH
43 CATERPILLAR INC CAT 149123101 $186.0M 0.61% 174,620 SH
44 SEMTECH CORP SMTC 816850101 $183.4M 0.60% 1,133,268 SH
45 AMETEK INC AME 031100100 $175.1M 0.57% 723,798 SH
46 ABIVAX SA ABVX 00370M103 $174.5M 0.57% 1,309,825 SH
47 INSMED INC INSM 457669307 $173.7M 0.57% 1,629,561 SH
48 ITT INC ITT 45073V108 $164.2M 0.54% 830,382 SH
49 GILEAD SCIENCES INC GILD 375558103 $162.7M 0.53% 1,287,629 SH
50 PTC THERAPEUTICS INC PTCT 69366J200 $159.6M 0.52% 1,956,156 SH
Filing History
Period Filed AUM Holdings Accession
2026-06-30 2026-08-12 $30.61B 278 0001177719-26-000021
2026-03-31 2026-05-11 $23.83B 250 0001177719-26-000018
2025-12-31 2026-02-11 $24.01B 241 0001177719-26-000005
2025-09-30 2025-11-12 $23.83B 235 0001177719-25-000003
Filer Information
Address
ONE FINANCIAL CENTER
23RD FLOOR
BOSTON, MA 02111
Phone
(617) 428-7100
Filing Manager
WESTFIELD CAPITAL MANAGEMENT CO LP
BOSTON, MA
Signatory
Brandi McMahon
Vice President, Deputy Chief Compliance Officer