WESTFIELD CAPITAL MANAGEMENT CO LP

BOSTON, MA · CIK 1177719 · 13F filing filed 2026-08-12

SEC-registered investment adviser since 2008 · limited partnership

Assets managed$29.8bn
Staff63 · 19 in investment roles
Main clients (by assets)Mutual funds and ETFs 34%, Pension plans 21%, Private funds 15%
Private funds2 (1 hedge) · $71.3m gross assets
Websitewestfieldcapital.com
Form ADV · 2026-07-01SEC adviser record

$30.6bn reported value +28.4% vs Q1 2026

278positions

29.2%in top 10

69 new 98 added 103 reduced 41 sold out vs Q1 2026

Holdings, Q2 2026

The small lines show how much was held over the last 4 quarters (adjusted for stock splits).

#	Security	Ticker	Shares	Value	% of portfolio	Change	Shares change
1	NVIDIA CORPORATION COM NVDA	NVDA	8,079,926	$1.6bn5.28%	5.28%	Added +1.8m	+1,762,887 27.9%
2	ALPHABET INC CAP STK CL A GOOGL	GOOGL	3,749,074	$1.3bn4.38%	4.38%	Added +1.7m	+1,722,330 85.0%
3	ASCENDIS PHARMA A/S ORD SHS ASND	ASND	4,798,267	$1.3bn4.18%	4.18%	New
4	AXON ENTERPRISE INC COM AXON	AXON	1,491,490	$836.1m2.73%	2.73%	Added +427.4k	+427,356 40.2%
5	FTAI AVIATION LTD SHS FTAI	FTAI	2,937,228	$794.6m2.60%	2.60%	Added +89.0k	+89,001 3.1%
6	APPLE INC COM AAPL	AAPL	2,573,774	$744.7m2.43%	2.43%	Reduced -559.3k	-559,339 -17.9%
7	COMFORT SYS USA INC COM FIX	FIX	355,433	$704.5m2.30%	2.30%	Reduced -265.5k	-265,482 -42.8%
8	BROADCOM INC COM AVGO	AVGO	1,556,522	$588.0m1.92%	1.92%	Added +319.6k	+319,597 25.8%
9	MICROSOFT CORP COM MSFT	MSFT	1,414,294	$527.6m1.72%	1.72%	Reduced -235.2k	-235,219 -14.3%
10	HOWMET AEROSPACE INC COM HWM	HWM	1,921,476	$516.6m1.69%	1.69%	Reduced -368.2k	-368,221 -16.1%
11	ELI LILLY & CO COM LLY	LLY	416,732	$499.8m1.63%	1.63%	Added +52.2k	+52,153 14.3%
12	SNOWFLAKE INC CL A SNOW	SNOW	1,736,498	$441.9m1.44%	1.44%	Added +1.0m	+1,017,688 141.6%
13	MKS INC. COM MKSI	MKSI	928,617	$413.0m1.35%	1.35%	Reduced -118.1k	-118,146 -11.3%
14	META PLATFORMS INC CL A META	META	677,389	$381.6m1.25%	1.25%	Added +150.6k	+150,567 28.6%
15	VERTIV HOLDINGS CO COM CL A VRT	VRT	1,054,361	$353.0m1.15%	1.15%	Reduced -867.3k	-867,335 -45.1%
16	GE VERNOVA INC COM GEV	GEV	241,272	$283.5m0.93%	0.93%	Added +42.0k	+41,966 21.1%
17	MICRON TECHNOLOGY INC COM MU	MU	228,203	$263.4m0.86%	0.86%	Added +127.8k	+127,769 127.2%
18	VISA INC COM CL A V	V	762,403	$261.6m0.85%	0.85%	Added +305.9k	+305,855 67.0%
19	API GROUP CORP COM STK APG	APG	6,154,301	$260.6m0.85%	0.85%	Added +1.5m	+1,519,372 32.8%
20	TAPESTRY INC COM TPR	TPR	1,696,569	$248.3m0.81%	0.81%	Reduced -502.3k	-502,293 -22.8%
21	RHYTHM PHARMACEUTICALS INC COM RYTM	RYTM	2,208,595	$245.2m0.80%	0.80%	Added +279.5k	+279,472 14.5%
22	LIFE TIME GROUP HOLDINGS INC COMMON STOCK LTH	LTH	5,995,254	$244.8m0.80%	0.80%	Added +2.8m	+2,809,739 88.2%
23	TAIWAN SEMICONDUCTOR MFG LTD SPONSORED ADS TSM	TSM	510,999	$244.0m0.80%	0.80%	Added +17.5k	+17,495 3.5%
24	GUARDANT HEALTH INC COM GH	GH	1,624,459	$243.7m0.80%	0.80%	Added +261.9k	+261,920 19.2%
25	QUANTA SVCS INC COM PWR	PWR	331,489	$238.7m0.78%	0.78%	Reduced -327	-327 -0.1%
26	SERVICENOW INC COM NOW	NOW	2,373,711	$235.7m0.77%	0.77%	Added +979.5k	+979,524 70.3%
27	ADVANCED MICRO DEVICES INC COM AMD	AMD	403,081	$234.2m0.76%	0.76%	Added +398.1k	+398,061 7929.5%
28	PALO ALTO NETWORKS INC COM PANW	PANW	658,331	$224.5m0.73%	0.73%	Added +21.8k	+21,848 3.4%
29	WOODWARD INC COM WWD	WWD	526,505	$224.0m0.73%	0.73%	Added +254.3k	+254,320 93.4%
30	ARISTA NETWORKS INC COM SHS ANET	ANET	1,317,096	$223.7m0.73%	0.73%	Added +536.7k	+536,694 68.8%
31	LPL FINL HLDGS INC COM LPLA	LPLA	793,061	$223.4m0.73%	0.73%	Reduced -88.4k	-88,445 -10.0%
32	ROCKET LAB CORP COM RKLB	RKLB	2,114,005	$214.9m0.70%	0.70%	Reduced -1.1m	-1,058,606 -33.4%
33	AMER SPORTS INC COM SHS AS	AS	6,344,923	$214.7m0.70%	0.70%	Added +2.4m	+2,407,402 61.1%
34	CLOUDFLARE INC CL A COM NET	NET	835,502	$204.9m0.67%	0.67%	Added +293.9k	+293,936 54.3%
35	AMAZON COM INC COM AMZN	AMZN	859,806	$204.9m0.67%	0.67%	Reduced -1.4m	-1,419,848 -62.3%
36	GARMIN LTD SHS GRMN	GRMN	861,057	$204.5m0.67%	0.67%	Added +484.7k	+484,695 128.8%
37	REGAL REXNORD CORPORATION COM RRX	RRX	856,976	$204.1m0.67%	0.67%	Added +175.3k	+175,259 25.7%
38	NATERA INC COM NTRA	NTRA	726,628	$197.2m0.64%	0.64%	Reduced -28.1k	-28,101 -3.7%
39	MORGAN STANLEY COM NEW MS	MS	940,560	$196.6m0.64%	0.64%	Added +444.0k	+444,002 89.4%
40	CARPENTER TECHNOLOGY CORP COM CRS	CRS	314,082	$193.7m0.63%	0.63%	New
41	SAMSARA INC COM CL A IOT	IOT	5,836,459	$189.3m0.62%	0.62%	Added +763.6k	+763,638 15.1%
42	DYNATRACE INC COM NEW DT	DT	4,249,229	$186.6m0.61%	0.61%	Added +39.6k	+39,635 0.9%
43	CATERPILLAR INC COM CAT	CAT	174,620	$186.0m0.61%	0.61%	Added +142.3k	+142,295 440.2%
44	SEMTECH CORP COM SMTC	SMTC	1,133,268	$183.4m0.60%	0.60%	Reduced -147.3k	-147,326 -11.5%
45	AMETEK INC COM AME	AME	723,798	$175.1m0.57%	0.57%	Reduced -22.0k	-22,034 -3.0%
46	ABIVAX SA SPONSORED ADS ABVX	ABVX	1,309,825	$174.5m0.57%	0.57%	Reduced -13.1k	-13,113 -1.0%
47	INSMED INC COM PAR $.01 INSM	INSM	1,629,561	$173.7m0.57%	0.57%	Added +161.1k	+161,102 11.0%
48	ITT INC COM ITT	ITT	830,382	$164.2m0.54%	0.54%	Added +127.1k	+127,073 18.1%
49	GILEAD SCIENCES INC COM GILD	GILD	1,287,629	$162.7m0.53%	0.53%	Added +1.3m	+1,260,939 4724.4%
50	PTC THERAPEUTICS INC COM PTCT	PTCT	1,956,156	$159.6m0.52%	0.52%	New
51	DUTCH BROS INC CL A BROS	BROS	2,184,001	$156.8m0.51%	0.51%	Reduced -129.4k	-129,356 -5.6%
52	CELSIUS HLDGS INC COM NEW CELH	CELH	5,324,481	$155.9m0.51%	0.51%	Added +1.6m	+1,555,570 41.3%
53	MASTEC INC COM MTZ	MTZ	374,457	$155.8m0.51%	0.51%	Added +124.5k	+124,477 49.8%
54	SHARKNINJA INC COM SHS SN	SN	1,008,349	$153.5m0.50%	0.50%	Added +103.8k	+103,808 11.5%
55	CSX CORP COM CSX	CSX	3,154,419	$149.9m0.49%	0.49%	Added +1.5m	+1,496,120 90.2%
56	FIRSTCASH HOLDINGS INC COM FCFS	FCFS	693,085	$149.9m0.49%	0.49%	Added +261.1k	+261,092 60.4%
57	KEYCORP COM KEY	KEY	6,493,467	$149.7m0.49%	0.49%	Added +1.3m	+1,300,133 25.0%
58	MICROCHIP TECHNOLOGY INC. COM MCHP	MCHP	1,639,111	$149.5m0.49%	0.49%	Added +668.8k	+668,816 68.9%
59	APPLIED MATLS INC COM AMAT	AMAT	205,592	$148.6m0.49%	0.49%	Added +204.7k	+204,656 21865.0%
60	MARRIOTT INTL INC NEW CL A MAR	MAR	398,962	$147.9m0.48%	0.48%	Added +245.7k	+245,743 160.4%
61	VAXCYTE INC COM PCVX	PCVX	2,472,428	$143.7m0.47%	0.47%	Reduced -1.2m	-1,173,710 -32.2%
62	GLOBE LIFE INC COM GL	GL	770,990	$137.8m0.45%	0.45%	Reduced -71.4k	-71,433 -8.5%
63	TECHNIPFMC PLC COM FTI	FTI	2,059,689	$136.6m0.45%	0.45%	Added +25.9k	+25,934 1.3%
64	XPO INC COM XPO	XPO	629,011	$129.1m0.42%	0.42%	Added +57.0k	+57,019 10.0%
65	LEGEND BIOTECH CORP SPONSORED ADS LEGN	LEGN	4,430,063	$127.9m0.42%	0.42%	Reduced -1.3m	-1,333,412 -23.1%
66	PURE STORAGE INC CL A P	P	1,611,958	$127.0m0.41%	0.41%	Reduced -262.8k	-262,805 -14.0%
67	LAM RESEARCH CORP COM NEW LRCX	LRCX	285,614	$123.8m0.40%	0.40%	New
68	JONES LANG LASALLE INC COM JLL	JLL	398,453	$123.5m0.40%	0.40%	Added +50.7k	+50,674 14.6%
69	ASTERA LABS INC COM ALAB	ALAB	249,299	$120.4m0.39%	0.39%	Reduced -610.8k	-610,814 -71.0%
70	ROCKWELL AUTOMATION INC COM ROK	ROK	237,136	$117.4m0.38%	0.38%	Added +30.9k	+30,859 15.0%
71	IDEX CORP COM IEX	IEX	513,564	$116.6m0.38%	0.38%	Added +87.5k	+87,545 20.6%
72	COHERENT CORP COM COHR	COHR	291,040	$114.8m0.38%	0.38%	Reduced -105.6k	-105,604 -26.6%
73	LEGENCE CORP CL A LGN	LGN	1,341,963	$114.4m0.37%	0.37%	Reduced -519.7k	-519,690 -27.9%
74	LINCOLN ELEC HLDGS INC COM LECO	LECO	430,681	$114.4m0.37%	0.37%	Added +72.5k	+72,516 20.2%
75	ASML HOLDING N V N Y REGISTRY SHS ASML	ASML	57,430	$114.3m0.37%	0.37%	New
76	PLANET LABS PBC COM CL A PL	PL	3,428,007	$113.6m0.37%	0.37%	Added +1.8m	+1,790,966 109.4%
77	ONTO INNOVATION INC COM ONTO	ONTO	299,383	$113.3m0.37%	0.37%	Reduced -27.6k	-27,577 -8.4%
78	CENCORA INC COM COR	COR	400,058	$113.2m0.37%	0.37%	Reduced -36.9k	-36,851 -8.4%
79	REVOLUTION MEDICINES INC COM RVMD	RVMD	600,821	$112.5m0.37%	0.37%	Reduced -955.8k	-955,757 -61.4%
80	SANDISK CORP COM SNDK	SNDK	49,024	$111.5m0.36%	0.36%	New
81	AFFIRM HLDGS INC COM CL A AFRM	AFRM	1,352,200	$110.3m0.36%	0.36%	Added +271.6k	+271,564 25.1%
82	LIVE NATION ENTERTAINMENT IN COM LYV	LYV	590,764	$108.2m0.35%	0.35%	Reduced -219.9k	-219,946 -27.1%
83	ENPRO INC COM NPO	NPO	286,554	$108.0m0.35%	0.35%	New
84	PERMIAN RESOURCES CORP CLASS A COM PR	PR	5,756,888	$106.0m0.35%	0.35%	Reduced -1.7m	-1,724,569 -23.1%
85	ARES MANAGEMENT CORPORATION CL A COM STK ARES	ARES	952,032	$106.0m0.35%	0.35%	Reduced -620.8k	-620,755 -39.5%
86	IMAX CORP COM IMAX	IMAX	2,654,014	$105.8m0.35%	0.35%	Added +315.2k	+315,238 13.5%
87	GUIDEWIRE SOFTWARE INC COM GWRE	GWRE	839,337	$103.3m0.34%	0.34%	Added +352.8k	+352,756 72.5%
88	NEXTRACKER INC CLASS A COM NXT	NXT	857,399	$102.2m0.33%	0.33%	Reduced -249.9k	-249,947 -22.6%
89	JFROG LTD ORD SHS FROG	FROG	1,114,561	$101.3m0.33%	0.33%	New
90	SYNOPSYS INC COM SNPS	SNPS	226,856	$101.2m0.33%	0.33%	Added +94.0k	+94,008 70.8%
91	ROKU INC COM CL A ROKU	ROKU	716,557	$99.0m0.32%	0.32%	Reduced -461.7k	-461,662 -39.2%
92	PLEXUS CORP COM PLXS	PLXS	321,808	$96.8m0.32%	0.32%	Reduced -62.7k	-62,685 -16.3%
93	APPLIED INDL TECHNOLOGIES IN COM AIT	AIT	285,691	$96.6m0.32%	0.32%	Reduced -3.5k	-3,510 -1.2%
94	MSCI INC COM MSCI	MSCI	171,958	$96.3m0.31%	0.31%	Reduced -61.8k	-61,806 -26.4%
95	ROBINHOOD MKTS INC COM CL A HOOD	HOOD	955,544	$95.8m0.31%	0.31%	Added +322.2k	+322,160 50.9%
96	ROSS STORES INC COM ROST	ROST	442,420	$94.2m0.31%	0.31%	Reduced -29.5k	-29,496 -6.2%
97	ADAPTIVE BIOTECHNOLOGIES COR COM ADPT	ADPT	4,267,645	$91.5m0.30%	0.30%	Reduced -1.2m	-1,169,073 -21.5%
98	XENON PHARMACEUTICALS INC COM XENE	XENE	1,507,294	$91.0m0.30%	0.30%	Added +105.8k	+105,811 7.5%
99	OREILLY AUTOMOTIVE INC COM ORLY	ORLY	933,255	$85.9m0.28%	0.28%	Added +45.3k	+45,256 5.1%
100	CITIGROUP INC COM NEW C	C	608,124	$85.1m0.28%	0.28%	Added +563.7k	+563,667 1267.9%

Sold out since Q1 2026

Security	Ticker	Shares held before	Value then
ASCENDIS PHARMA A/S		4,813,440	$1.1bn4.8m shares
KRATOS DEFENSE & SEC SOLUTIO KTOS	KTOS	1,563,146	$110.2m1.6m shares
AMERICAN INTL GROUP INC AIG	AIG	1,458,711	$109.8m1.5m shares
PALANTIR TECHNOLOGIES INC PLTR	PLTR	674,557	$98.7m674.6k shares
GENEDX HOLDINGS CORP WGS	WGS	1,369,108	$87.9m1.4m shares
F5 INC FFIV	FFIV	298,542	$86.4m298.5k shares
C H ROBINSON WORLDWIDE INC CHRW	CHRW	429,500	$71.3m429.5k shares
LOWES COS INC LOW	LOW	300,962	$71.1m301.0k shares
MASIMO CORP MASI	MASI	341,229	$60.7m341.2k shares
ZSCALER INC ZS	ZS	427,919	$60.0m427.9k shares
HUBSPOT INC HUBS	HUBS	232,976	$56.9m233.0k shares
INSTALLED BLDG PRODS INC IBP	IBP	208,248	$55.2m208.2k shares
MOODYS CORP MCO	MCO	123,603	$53.9m123.6k shares
TOPBUILD CORP BLD	BLD	148,581	$52.2m148.6k shares
KKR & CO INC KKR	KKR	558,136	$51.6m558.1k shares
BIO-TECHNE CORP TECH	TECH	856,043	$44.7m856.0k shares
FAIR ISAAC CORP FICO	FICO	39,934	$42.6m39.9k shares
IONQ INC IONQ	IONQ	1,373,788	$39.6m1.4m shares
HAMILTON LANE INC HLNE	HLNE	364,174	$36.2m364.2k shares
OPTION CARE HEALTH INC OPCH	OPCH	1,182,814	$31.8m1.2m shares
TRANSDIGM GROUP INC TDG	TDG	12,950	$15.0m12.9k shares
WELLS FARGO CO NEW WFC	WFC	87,713	$7.0m87.7k shares
M & T BK CORP MTB	MTB	29,839	$6.2m29.8k shares
RAYMOND JAMES FINL INC RJF	RJF	40,095	$5.8m40.1k shares
MCDONALDS CORP MCD	MCD	18,034	$5.6m18.0k shares

Stakes above 5%

Companies where this manager has reported owning more than 5% of a class of shares, on Schedule 13D (may seek influence) or 13G (passive): its latest filing for each, from 19 Dec 2024 on.

Company	Ticker	Stake	Change	Schedule	Last filed
ASCENDIS PHARMA A/S 13G · filed 2026-02-11		8.5%	-0.7 pts	13G	2026-02-11