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Westfield Capital Management Co. LP

Form 13F · CIK 1177719. Holdings on 30 Jun 2026, as filed with the SEC on 12 Aug 2026, each set beside the March 2026 quarter. The 13F on the SEC's site.

Westfield Capital Management Co. LP reported 278 positions worth $30.6B for the June 2026 quarter, on a Form 13F filed 12 Aug 2026; the largest holding was NVIDIA Corp., at 5.3% of the fund.

What it bought and sold

The largest moves since the March 2026 quarter, by the dollars that moved: 68 opened, 97 added, 100 trimmed, 40 sold out.

New position: 68

CompanyValueChange in shares
Carpenter Technology Corp. (CRS)$193.7M+314,082
PTC Therapeutics, Inc. (PTCT)$159.6M+1,956,156
Lam Research Corp. (LRCX)$123.8M+285,614
ASML Holding N.V. (ASML)$114.3M+57,430
Sandisk Corp. (SNDK)$111.5M+49,024
Enpro Inc. (NPO)$108.0M+286,554
JFrog Ltd. (FROG)$101.3M+1,114,561
TTM Technologies Inc. (TTMI)$77.8M+416,052
Forgent Power Solutions Inc (FPS)$76.6M+1,370,928
Rubrik, Inc. (RBRK)$75.2M+937,308

Added: 97

CompanyValueChange in shares
Alphabet Inc. (GOOGL)$1.3B+1,722,330
NVIDIA Corp. (NVDA)$1.6B+1,762,887
Axon Enterprise, Inc. (AXON)$836.1M+427,356
Snowflake Inc. (SNOW)$441.9M+1,017,688
Advanced Micro Devices Inc. (AMD)$234.2M+398,061
Micron Technology Inc. (MU)$263.4M+127,769
Broadcom Inc. (AVGO)$588.0M+319,597
Eli Lilly & Co. (LLY)$499.8M+52,153
Caterpillar Inc. (CAT)$186.0M+142,295
Life Time Group Holdings, Inc. (LTH)$244.8M+2,809,739

Trimmed: 100

CompanyValueChange in shares
Amazon.com Inc. (AMZN)$204.9M-1,419,848
Ascendis Pharma A/s (ASND)$1.3B-15,173
MKS Inc. (MKSI)$413.0M-118,146
Netflix Inc. (NFLX)$20.8M-1,679,161
Marvell Technology, Inc. (MRVL)$3.9M-1,660,188
Bloom Energy Corp. (BE)$3.2M-1,181,002
Comfort Systems USA Inc. (FIX)$704.5M-265,482
Vertiv Holdings Co. (VRT)$353.0M-867,335
Royal Caribbean Cruises Ltd. (RCL)$40.7M-377,600
Tesla, Inc. (TSLA)$21.2M-265,691

Sold out: 40

CompanyValue a quarter beforeChange in shares
Kratos Defense & Security Solutions, Inc. (KTOS)$110.2M-1,563,146
American International Group, Inc. (AIG)$109.8M-1,458,711
Palantir Technologies Inc. (PLTR)$98.7M-674,557
GeneDx Holdings Corp. (WGS)$87.9M-1,369,108
F5, Inc. (FFIV)$86.4M-298,542
C. H. Robinson Worldwide, Inc. (CHRW)$71.3M-429,500
Lowe's Companies Inc. (LOW)$71.1M-300,962
Masimo Corp. (MASI)$60.7M-341,229
Zscaler, Inc. (ZS)$60.0M-427,919
Hubspot Inc. (HUBS)$56.9M-232,976

Largest holdings

The 100 largest of 278, by value.

CompanyValueOf the fundSharesChange in sharesMove
NVIDIA Corp. (NVDA)$1.6B5.28%8,079,926+1,762,887Added
Alphabet Inc. (GOOGL)$1.3B4.38%3,749,074+1,722,330Added
Ascendis Pharma A/s (ASND)$1.3B4.18%4,798,267-15,173Trimmed
Axon Enterprise, Inc. (AXON)$836.1M2.73%1,491,490+427,356Added
Ftai Aviation Ltd. (FTAI)$794.6M2.60%2,937,228+89,001Added
Apple Inc. (AAPL)$744.7M2.43%2,573,774-559,339Trimmed
Comfort Systems USA Inc. (FIX)$704.5M2.30%355,433-265,482Trimmed
Broadcom Inc. (AVGO)$588.0M1.92%1,556,522+319,597Added
Microsoft Corp. (MSFT)$527.6M1.72%1,414,294-235,219Trimmed
Howmet Aerospace Inc. (HWM)$516.6M1.69%1,921,476-368,221Trimmed
Eli Lilly & Co. (LLY)$499.8M1.63%416,732+52,153Added
Snowflake Inc. (SNOW)$441.9M1.44%1,736,498+1,017,688Added
MKS Inc. (MKSI)$413.0M1.35%928,617-118,146Trimmed
Meta Platforms, Inc. (META)$381.6M1.25%677,389+150,567Added
Vertiv Holdings Co. (VRT)$353.0M1.15%1,054,361-867,335Trimmed
GE Vernova Inc. (GEV)$283.5M0.93%241,272+41,966Added
Micron Technology Inc. (MU)$263.4M0.86%228,203+127,769Added
Visa Inc. (V)$261.6M0.85%762,403+305,855Added
APi Group Corp. (APG)$260.6M0.85%6,154,301+1,519,372Added
Tapestry, Inc. (TPR)$248.3M0.81%1,696,569-502,293Trimmed
Rhythm Pharmaceuticals, Inc. (RYTM)$245.2M0.80%2,208,595+279,472Added
Life Time Group Holdings, Inc. (LTH)$244.8M0.80%5,995,254+2,809,739Added
Taiwan Semiconductor Manufacturing Company Limited (TSM)$244.0M0.80%510,999+17,495Added
Guardant Health, Inc. (GH)$243.7M0.80%1,624,459+261,920Added
Quanta Services, Inc. (PWR)$238.7M0.78%331,489-327Held
ServiceNow, Inc. (NOW)$235.7M0.77%2,373,711+979,524Added
Advanced Micro Devices Inc. (AMD)$234.2M0.77%403,081+398,061Added
Palo Alto Networks Inc. (PANW)$224.5M0.73%658,331+21,848Added
Woodward, Inc. (WWD)$224.0M0.73%526,505+254,320Added
Arista Networks, Inc. (ANET)$223.7M0.73%1,317,096+536,694Added
LPL Financial Holdings Inc. (LPLA)$223.4M0.73%793,061-88,445Trimmed
Rocket Lab Corp. (RKLB)$214.9M0.70%2,114,005-1,058,606Trimmed
Amer Sports Inc. (AS)$214.7M0.70%6,344,923+2,407,402Added
Cloudflare, Inc. (NET)$204.9M0.67%835,502+293,936Added
Amazon.com Inc. (AMZN)$204.9M0.67%859,806-1,419,848Trimmed
Garmin Ltd. (GRMN)$204.5M0.67%861,057+484,695Added
Regal Rexnord Corp. (RRX)$204.1M0.67%856,976+175,259Added
Natera, Inc. (NTRA)$197.2M0.64%726,628-28,101Trimmed
Morgan Stanley (MS)$196.6M0.64%940,560+444,002Added
Carpenter Technology Corp. (CRS)$193.7M0.63%314,082+314,082New position
Samsara Inc. (IOT)$189.3M0.62%5,836,459+763,638Added
Dynatrace, Inc. (DT)$186.6M0.61%4,249,229+39,635Added
Caterpillar Inc. (CAT)$186.0M0.61%174,620+142,295Added
Semtech Corp. (SMTC)$183.4M0.60%1,133,268-147,326Trimmed
AMETEK Inc. (AME)$175.1M0.57%723,798-22,034Trimmed
Abivax SA (ABVX)$174.5M0.57%1,309,825-13,113Trimmed
Insmed Inc. (INSM)$173.7M0.57%1,629,561+161,102Added
ITT Inc. (ITT)$164.2M0.54%830,382+127,073Added
Gilead Sciences, Inc. (GILD)$162.7M0.53%1,287,629+1,260,939Added
PTC Therapeutics, Inc. (PTCT)$159.6M0.52%1,956,156+1,956,156New position
Dutch Bros Inc. (BROS)$156.8M0.51%2,184,001-129,356Trimmed
Celsius Holdings, Inc. (CELH)$155.9M0.51%5,324,481+1,555,570Added
Mastec Inc. (MTZ)$155.8M0.51%374,457+124,477Added
SharkNinja, Inc. (SN)$153.5M0.50%1,008,349+103,808Added
CSX Corp. (CSX)$149.9M0.49%3,154,419+1,496,120Added
FirstCash Holdings, Inc. (FCFS)$149.9M0.49%693,085+261,092Added
Keycorp (KEY)$149.7M0.49%6,493,467+1,300,133Added
Microchip Technology Inc. (MCHP)$149.5M0.49%1,639,111+668,816Added
Applied Materials Inc. (AMAT)$148.6M0.49%205,592+204,656Added
Marriott International Inc. (MAR)$147.9M0.48%398,962+245,743Added
Vaxcyte Inc. (PCVX)$143.7M0.47%2,472,428-1,173,710Trimmed
Globe Life Inc. (GL)$137.8M0.45%770,990-71,433Trimmed
TechnipFMC plc (FTI)$136.6M0.45%2,059,689+25,934Added
Xpo, Inc. (XPO)$129.1M0.42%629,011+57,019Added
Legend Biotech Corp. (LEGN)$127.9M0.42%4,430,063-1,333,412Trimmed
Everpure, Inc. (P)$127.0M0.41%1,611,958-262,805Trimmed
Lam Research Corp. (LRCX)$123.8M0.40%285,614+285,614New position
Jones Lang Lasalle Inc. (JLL)$123.5M0.40%398,453+50,674Added
Astera Labs, Inc. (ALAB)$120.4M0.39%249,299-610,814Trimmed
Rockwell Automation, Inc. (ROK)$117.4M0.38%237,136+30,859Added
Idex Corp. (IEX)$116.6M0.38%513,564+87,545Added
Coherent Corp. (COHR)$114.8M0.38%291,040-105,604Trimmed
Legence Corp. (LGN)$114.4M0.37%1,341,963-519,690Trimmed
Lincoln Electric Holdings Inc. (LECO)$114.4M0.37%430,681+72,516Added
ASML Holding N.V. (ASML)$114.3M0.37%57,430+57,430New position
Planet Labs PBC (PL)$113.6M0.37%3,428,007+1,790,966Added
Onto Innovation Inc. (ONTO)$113.3M0.37%299,383-27,577Trimmed
Cencora, Inc. (COR)$113.2M0.37%400,058-36,851Trimmed
Revolution Medicines, Inc. (RVMD)$112.5M0.37%600,821-955,757Trimmed
Sandisk Corp. (SNDK)$111.5M0.36%49,024+49,024New position
Affirm Holdings, Inc. (AFRM)$110.3M0.36%1,352,200+271,564Added
Live Nation Entertainment, Inc. (LYV)$108.2M0.35%590,764-219,946Trimmed
Enpro Inc. (NPO)$108.0M0.35%286,554+286,554New position
Permian Resources Corp. (PR)$106.0M0.35%5,756,888-1,724,569Trimmed
Ares Management Corp. (ARES)$106.0M0.35%952,032-620,755Trimmed
Imax Corp. (IMAX)$105.8M0.35%2,654,014+315,238Added
Guidewire Software, Inc. (GWRE)$103.3M0.34%839,337+352,756Added
Nextpower Inc. (NXT)$102.2M0.33%857,399-249,947Trimmed
JFrog Ltd. (FROG)$101.3M0.33%1,114,561+1,114,561New position
Synopsys Inc. (SNPS)$101.2M0.33%226,856+94,008Added
Roku, Inc. (ROKU)$99.0M0.32%716,557-461,662Trimmed
Plexus Corp. (PLXS)$96.8M0.32%321,808-62,685Trimmed
Applied Industrial Technologies Inc. (AIT)$96.6M0.32%285,691-3,510Trimmed
MSCI Inc. (MSCI)$96.3M0.32%171,958-61,806Trimmed
Robinhood Markets, Inc. (HOOD)$95.8M0.31%955,544+322,160Added
ROSS Stores, Inc. (ROST)$94.2M0.31%442,420-29,496Trimmed
Adaptive Biotechnologies Corp. (ADPT)$91.5M0.30%4,267,645-1,169,073Trimmed
Xenon Pharmaceuticals Inc. (XENE)$91.0M0.30%1,507,294+105,811Added
O'Reilly Automotive, Inc. (ORLY)$85.9M0.28%933,255+45,256Added
Citigroup Inc. (C)$85.1M0.28%608,124+563,667Added

Every quarter it filed

What the fund reported and how many positions it held, each quarter since September 2024.

QuarterReported valuePositions
June 2026 quarter$30.6B278
March 2026 quarter$23.8B250
December 2025 quarter$24.0B241
September 2025 quarter$23.8B235
June 2025 quarter$23.8B239
March 2025 quarter$20.5B244
December 2024 quarter$23.0B239
September 2024 quarter$22.1B247
Every 13F fund · Fund holdings data