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WESTFIELD CAPITAL MANAGEMENT CO LP

Quarterly 13F snapshot: US-listed longs only, no performance figures — 13F data cannot support them.

Portfolio value
$30.6B
Positions
278
Quarter ended
June 30, 2026
Filed
August 12, 2026

Reported portfolio value by quarter (53 quarters reported)

$30.6B $11.4B
Q2 13 Q1 16 Q4 18 Q3 21 Q2 24 Q2 26

$14.5B in Q2 2013 → $30.6B now. Hover for any quarter.

Holdings

As reported for the quarter ended June 30, 2026. Activity is the change in share count since the prior quarter's filing.

Holding % of portfolio Activity Shares Value
Nvidia Corporation 5.3% Added 28% 8,079,926 $1.62B
Alphabet Inc 4.4% Added 85% 3,749,074 $1.34B
Ascendis Pharma A/s 4.2% New 4,798,267 $1.28B
Axon Enterprise Inc 2.7% Added 40% 1,491,490 $836M
Ftai Aviation Ltd 2.6% Added 3.1% 2,937,228 $795M
Apple Inc 2.4% Trimmed 18% 2,573,774 $745M
CS Comfort Sys Usa Inc 2.3% Trimmed 43% 355,433 $704M
Broadcom Inc 1.9% Added 26% 1,556,522 $588M
Microsoft Corp 1.7% Trimmed 14% 1,414,294 $528M
Howmet Aerospace Inc 1.7% Trimmed 16% 1,921,476 $517M
Eli Lilly & Co 1.6% Added 14% 416,732 $500M
Snowflake Inc 1.4% Added 142% 1,736,498 $442M
Mks Inc. 1.3% Trimmed 11% 928,617 $413M
Meta Platforms Inc 1.2% Added 29% 677,389 $382M
Vertiv Holdings Co 1.2% Trimmed 45% 1,054,361 $353M
Ge Vernova Inc 0.9% Added 21% 241,272 $283M
Micron Technology Inc 0.9% Added 127% 228,203 $263M
Visa Inc 0.9% Added 67% 762,403 $262M
Api Group Corp 0.9% Added 33% 6,154,301 $261M
Tapestry Inc 0.8% Trimmed 23% 1,696,569 $248M
Rhythm Pharmaceuticals Inc 0.8% Added 14% 2,208,595 $245M
Life Time Group Holdings Inc 0.8% Added 88% 5,995,254 $245M
TS Taiwan Semiconductor Manufac 0.8% Added 3.5% 510,999 $244M
Guardant Health Inc 0.8% Added 19% 1,624,459 $244M
QS Quanta Svcs Inc 0.8% Trimmed 0.1% 331,489 $239M
Servicenow Inc 0.8% Added 70% 2,373,711 $236M
Advanced Micro Devices Inc 0.8% Added 7930% 403,081 $234M
Palo Alto Networks Inc 0.7% Added 3.4% 658,331 $225M
Woodward Inc 0.7% Added 93% 526,505 $224M
Arista Networks Inc 0.7% Added 69% 1,317,096 $224M
LF Lpl Finl Hldgs Inc 0.7% Trimmed 10% 793,061 $223M
Rocket Lab Corp 0.7% Trimmed 33% 2,114,005 $215M
Amer Sports Inc 0.7% Added 61% 6,344,923 $215M
Cloudflare Inc 0.7% Added 54% 835,502 $205M
Amazon Com Inc 0.7% Trimmed 62% 859,806 $205M
Garmin Ltd 0.7% Added 129% 861,057 $205M
Regal Rexnord Corporation 0.7% Added 26% 856,976 $204M
Natera Inc 0.6% Trimmed 3.7% 726,628 $197M
Morgan Stanley 0.6% Added 89% 940,560 $197M
Carpenter Technology Corp 0.6% New 314,082 $194M
Samsara Inc 0.6% Added 15% 5,836,459 $189M
Dynatrace Inc 0.6% Added 0.9% 4,249,229 $187M
Caterpillar Inc 0.6% Added 440% 174,620 $186M
Semtech Corp 0.6% Trimmed 12% 1,133,268 $183M
Ametek Inc 0.6% Trimmed 3.0% 723,798 $175M
Abivax Sa 0.6% Trimmed 1.0% 1,309,825 $175M
Insmed Inc 0.6% Added 11% 1,629,561 $174M
Itt Inc 0.5% Added 18% 830,382 $164M
Gilead Sciences Inc 0.5% Added 4724% 1,287,629 $163M
Ptc Therapeutics Inc 0.5% New 1,956,156 $160M
Dutch Bros Inc 0.5% Trimmed 5.6% 2,184,001 $157M
CH Celsius Hldgs Inc 0.5% Added 41% 5,324,481 $156M
Mastec Inc 0.5% Added 50% 374,457 $156M
Sharkninja Inc 0.5% Added 11% 1,008,349 $154M
Csx Corp 0.5% Added 90% 3,154,419 $150M
Firstcash Holdings Inc 0.5% Added 60% 693,085 $150M
K Keycorp 0.5% Added 25% 6,493,467 $150M
Microchip Technology Inc. 0.5% Added 69% 1,639,111 $149M
AM Applied Matls Inc 0.5% Added 21865% 205,592 $149M
MI Marriott Intl Inc New 0.5% Added 160% 398,962 $148M

Showing top 60 of 278 positions.

Timeline of changes

What changed each quarter, from the filings' own share counts. Largest moves first; most recent 8 quarters.

Q2 2026

quarter ended June 30, 2026 · filed August 12, 2026

Company Action Shares changed Value of change % of portfolio
Ascendis Pharma A/s New +4,798,267 +$1.28B 4.2%
Ascendis Pharma A/s Exited −4,813,440 −$1.1B
Alphabet Inc Added +1,722,330 +$616M 4.4%
CS Comfort Sys Usa Inc Trimmed −265,482 −$526M 2.3%
Marvell Technology Inc Trimmed −1,660,188 −$495M
Bloom Energy Corp Trimmed −1,181,002 −$357M
Nvidia Corporation Added +1,762,887 +$353M 5.3%
Amazon Com Inc Trimmed −1,419,848 −$338M 0.7%
Astera Labs Inc Trimmed −610,814 −$295M 0.4%
Vertiv Holdings Co Trimmed −867,335 −$290M 1.2%

Showing the 10 largest of 311 changes.

Q1 2026

quarter ended March 31, 2026 · filed May 11, 2026

Company Action Shares changed Value of change % of portfolio
Masimo Corp Trimmed −1,180,820 −$210M 0.3%
Insmed Inc Added +1,035,938 +$169M 1.0%
BA Bank America Corp Trimmed −2,756,724 −$134M 0.2%
CS Commvault Sys Inc Exited −1,057,077 −$133M
Atlassian Corporation Exited −812,215 −$132M
Cheniere Energy Inc New +459,044 +$130M 0.5%
Amer Sports Inc New +3,937,521 +$130M 0.5%
Adma Biologics Inc Exited −6,992,907 −$128M
Revolution Medicines Inc Trimmed −1,288,435 −$125M 0.6%
Ftai Aviation Ltd Added +497,602 +$122M 2.9%

Showing the 10 largest of 278 changes.

Q4 2025

quarter ended December 31, 2025 · filed February 11, 2026

Company Action Shares changed Value of change % of portfolio
Transdigm Group Inc Trimmed −201,704 −$268M 0.1%
Merus N V Exited −2,132,489 −$201M
Servicenow Inc Added +1,216,801 +$186M 0.9%
CS Comfort Sys Usa Inc Trimmed −164,360 −$153M 2.6%
Coherent Corp Trimmed −807,840 −$149M 0.5%
Abivax Sa New +1,009,966 +$136M 0.6%
Api Group Corp New +3,453,355 +$132M 0.6%
Netflix Inc Added +1,366,899 +$128M 0.6%
Ametek Inc Added +541,556 +$111M 0.8%
Dutch Bros Inc New +1,779,616 +$109M 0.5%

Showing the 10 largest of 260 changes.

Q3 2025

quarter ended September 30, 2025 · filed November 12, 2025

Company Action Shares changed Value of change % of portfolio
Marvell Technology Inc New +2,611,958 +$220M 0.9%
Nvidia Corporation Trimmed −1,038,180 −$194M 5.1%
Fabrinet Trimmed −500,308 −$182M 0.2%
Salesforce Inc Exited −647,474 −$177M
Badger Meter Inc Exited −612,809 −$150M
Bloom Energy Corp New +1,675,282 +$142M 0.6%
Texas Roadhouse Inc Exited −705,622 −$132M
AM Applied Matls Inc Exited −694,431 −$127M
Amazon Com Inc Trimmed −558,723 −$123M 2.3%
Insmed Inc Trimmed −851,361 −$123M 0.3%

Showing the 10 largest of 269 changes.

Q2 2025

quarter ended June 30, 2025 · filed August 12, 2025

Company Action Shares changed Value of change % of portfolio
Palantir Technologies Inc Trimmed −1,891,411 −$258M
Alphabet Inc Trimmed −888,279 −$157M 1.9%
Howmet Aerospace Inc Added +780,896 +$145M 1.5%
Autozone Inc New +38,182 +$142M 0.6%
DS Dicks Sporting Goods Inc Exited −630,566 −$127M
AM Applied Matls Inc Added +689,272 +$126M 0.5%
Roblox Corp New +1,141,073 +$120M 0.5%
Axon Enterprise Inc Trimmed −137,722 −$114M 2.7%
RC Royal Caribbean Group New +352,525 +$110M 0.5%
Atlassian Corporation Trimmed −530,420 −$108M 0.2%

Showing the 10 largest of 269 changes.

Q1 2025

quarter ended March 31, 2025 · filed May 09, 2025

Company Action Shares changed Value of change % of portfolio
Chipotle Mexican Grill Inc Exited −2,675,519 −$161M
Howmet Aerospace Inc New +1,135,059 +$147M 0.7%
CP Check Point Software Tech Lt Added +589,816 +$134M 1.0%
Flywire Corporation Exited −6,516,044 −$134M
Mongodb Inc New +733,787 +$129M 0.6%
DS Dicks Sporting Goods Inc Added +599,025 +$121M 0.6%
Block Inc Exited −1,416,339 −$120M
Ptc Inc Exited −634,650 −$117M
IP International Paper Co New +2,117,805 +$113M 0.5%
Axon Enterprise Inc Added +212,931 +$112M 2.4%

Showing the 10 largest of 274 changes.

Q4 2024

quarter ended December 31, 2024 · filed February 11, 2025

Company Action Shares changed Value of change % of portfolio
Axon Enterprise Inc Trimmed −460,458 −$274M 1.8%
Sap Se Trimmed −647,291 −$159M
Eli Lilly & Co Added +193,642 +$149M 0.7%
CD Cadence Design System Inc Exited −533,449 −$145M
Mongodb Inc Exited −496,248 −$134M
SC Sun Cmntys Inc Exited −959,879 −$130M
Tapestry Inc Added +1,905,851 +$125M 1.0%
AH Asml Holding N V Exited −148,377 −$124M
Glaukos Corp Added +804,614 +$121M 0.5%
Block Inc New +1,416,339 +$120M 0.5%

Showing the 10 largest of 265 changes.

Q3 2024

quarter ended September 30, 2024 · filed November 12, 2024

Company Action Shares changed Value of change % of portfolio
Netflix Inc New +314,226 +$223M 1.0%
Uber Technologies Inc Exited −2,827,566 −$206M
Broadcom Inc Added +1,140,633 +$197M 0.9%
Home Depot Inc Trimmed −303,020 −$123M
Sharkninja Inc New +1,056,738 +$115M 0.5%
Toll Brothers Inc New +722,130 +$112M 0.5%
Target Corp New +683,263 +$106M 0.5%
Ge Vernova Inc New +413,169 +$105M 0.5%
Ftai Aviation Ltd Added +773,017 +$103M 1.0%
Moog Inc New +507,019 +$102M 0.5%

Showing the 10 largest of 275 changes.

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