Westfield Capital Management Co. LP
In its 13F for Q1 2026 (holdings as of March 31, 2026, filed May 11, 2026), Westfield Capital Management Co. LP reported 250 stock positions worth $23.8 billion. Its top holding was Nvidia (NVDA) at 4.6% of the portfolio, followed by Ascendis Pharma A/S (ASND, 4.6%) and Comfort Systems USA (FIX, 3.6%). Compared with Q4 2025, it opened 46 new positions, sold out of 37, added to 118 and reduced 77. The biggest buy was Ftai Aviation (FTAI, shares +21%) and the biggest sale Bank of America (BAC, shares −72%).
- Most Recent 13F
- Q2 2026
- Location
- BOSTON, MA
- CIK
- 0001177719
- Portfolio Value
- $23.8B (Q1 2026)
- SEC Filing
- 0001177719-26-000018 ↗ filed May 11, 2026
Holdings Value
Holdings 250 stocks · $23.8B
| NVDA Nvidia Corp. | 4.62% | 6,317,039 | $1.1B | Add +6.2% |
| ASND Ascendis Pharma A/S | 4.62% | 4,813,440 | $1.1B | Reduce -7.2% |
| FIX Comfort Systems USA Inc. | 3.59% | 620,915 | $856.2M | Reduce -7.2% |
| AAPL Apple Inc. | 3.34% | 3,133,113 | $795.2M | Reduce -4.3% |
| FTAI Ftai Aviation Ltd. | 2.93% | 2,848,227 | $697.8M | Add +21.2% |
| MSFT Microsoft Corp. | 2.56% | 1,649,513 | $610.6M | Add +1.8% |
| GOOGL Alphabet Inc. Class A | 2.45% | 2,026,744 | $582.8M | Reduce -7.0% |
| HWM Howmet Aerospace Inc. | 2.21% | 2,289,697 | $527.7M | Add +3.2% |
| VRT Vertiv Holdings Co. Class A | 2.02% | 1,921,696 | $481.5M | Reduce -15.6% |
| AMZN Amazon.com Inc. | 1.99% | 2,279,654 | $474.8M | Reduce -2.2% |
| AXON Axon Enterprise Inc. | 1.90% | 1,064,134 | $451.9M | Add +28.0% |
| AVGO Broadcom Inc. | 1.61% | 1,236,925 | $382.8M | Add +11.2% |
| LLY Eli Lilly & Co. | 1.41% | 364,579 | $335.3M | Add +31.4% |
| TPR Tapestry Inc. | 1.30% | 2,198,862 | $310.3M | Add +4.8% |
| META Meta Platforms Inc. Class A | 1.26% | 526,822 | $301.4M | Reduce -19.6% |
| LPLA LPL Financial Holdings Inc. | 1.11% | 881,506 | $265.2M | Add +40.9% |
| MKSI MKS Inc. | 1.01% | 1,046,763 | $240.6M | Add +24.6% |
| INSM Insmed Inc. | 1.01% | 1,468,459 | $240.1M | Add +239.5% |
| PCVX Vaxcyte Inc. | 0.89% | 3,646,138 | $211.9M | Add +3.0% |
| RKLB Rocket Lab Corp. | 0.85% | 3,172,611 | $203.7M | Add +22.4% |
| NFLX Netflix Inc. | 0.79% | 1,969,994 | $189.4M | Add +23.3% |
| APG Api Group Corp. | 0.79% | 4,634,929 | $187.8M | Add +34.2% |
| PWR Quanta Services Inc. | 0.76% | 331,816 | $182.2M | Add +21.3% |
| GEV GE Vernova Inc. | 0.73% | 199,306 | $174.0M | Add +12.0% |
| ARES Ares Management Corp. Class A | 0.72% | 1,572,787 | $171.6M | Add +36.6% |
| RYTM Rhythm Pharmaceuticals Inc. | 0.70% | 1,929,123 | $167.8M | Add +52.2% |
| TSM Taiwan Semiconductor-SP ADR | 0.70% | 493,504 | $166.8M | Add +10.6% |
| MRVL Marvell Technology Inc. | 0.70% | 1,673,381 | $165.7M | Reduce -14.1% |
| BE Bloom Energy Corp. Class A | 0.68% | 1,191,572 | $161.4M | Add +4.0% |
| IOT Samsara Inc. Class A | 0.67% | 5,072,821 | $160.8M | Add +28.3% |
| AME Ametek Inc. | 0.67% | 745,832 | $159.9M | Reduce -17.1% |
| PR Permian Resources Corp. Class A | 0.67% | 7,481,457 | $159.5M | Add +25.7% |
| DT Dynatrace Inc. | 0.65% | 4,209,594 | $155.7M | Add +25.4% |
| RVMD Revolution Medicines Inc. | 0.64% | 1,556,578 | $151.4M | Reduce -45.3% |
| NTRA Natera Inc. | 0.63% | 754,729 | $150.9M | Add +5.6% |
| FN Fabrinet | 0.62% | 284,874 | $148.6M | Add +49.8% |
| ABVX Abivax SA-ADR | 0.62% | 1,322,938 | $147.3M | Add +31.0% |
| NOW ServiceNow Inc. | 0.61% | 1,394,187 | $145.8M | Reduce -5.6% |
| FTI Technipfmc PLC | 0.59% | 2,033,755 | $140.6M | Add +4.2% |
| RCL Royal Caribbean Cruises Ltd. | 0.58% | 505,765 | $139.2M | Add +12.7% |
| HLT Hilton Worldwide Holdings Inc. | 0.58% | 457,425 | $139.1M | Add +27.9% |
| V Visa Inc. Class A | 0.58% | 456,548 | $138.0M | Reduce -24.4% |
| COR Cencora Inc. | 0.58% | 436,909 | $137.3M | Add +36.9% |
| ITT Itt Inc. | 0.56% | 703,309 | $134.0M | Add +19.7% |
| CELH Celsius Holdings Inc. | 0.56% | 3,768,911 | $133.7M | Add +144.1% |
| NXT Nextpower Inc. | 0.56% | 1,107,346 | $133.5M | Add +1.6% |
| LNG Cheniere Energy Inc. | 0.55% | 459,044 | $130.3M | New |
| AS Amer Sports Inc. | 0.54% | 3,937,521 | $129.6M | New |
| RRX Regal Rexnord Corp. | 0.54% | 681,717 | $127.7M | Reduce -23.7% |
| MSCI MSCI Inc. | 0.53% | 233,764 | $126.0M | Add +12.5% |
| GH Guardant Health Inc. | 0.53% | 1,362,539 | $125.9M | Add +152.7% |
| LYV Live Nation Entertainment Inc. | 0.52% | 810,710 | $123.6M | Add +4.6% |
| TSLA Tesla Inc. | 0.49% | 316,102 | $117.5M | Reduce -31.5% |
| GL Globe Life Inc. | 0.49% | 842,423 | $117.2M | Add +38.4% |
| BROS Dutch Bros Inc. Class A | 0.49% | 2,313,357 | $117.2M | Add +30.0% |
| NET Cloudflare Inc. Class A | 0.47% | 541,566 | $111.7M | Add +4.3% |
| ROKU Roku Inc. | 0.47% | 1,178,219 | $111.5M | Add +5.9% |
| XPO Xpo Inc. | 0.47% | 571,992 | $111.3M | Reduce -21.0% |
| FITB Fifth Third Bancorp | 0.47% | 2,385,422 | $110.8M | Reduce -36.3% |
| P Everpure Inc. Class A | 0.46% | 1,874,763 | $110.7M | Add +23.3% |
| KTOS Kratos Defense & Security | 0.46% | 1,563,146 | $110.2M | Add +25.5% |
| AIG American International Group | 0.46% | 1,458,711 | $109.8M | New |
| SNOW Snowflake Inc. | 0.45% | 718,810 | $108.4M | Add +10.7% |
| PRIM Primoris Services Corp. | 0.45% | 743,269 | $106.3M | Reduce -21.9% |
| JLL Jones Lang Lasalle Inc. | 0.44% | 347,779 | $105.8M | New |
| LGN Legence Corp. Class A | 0.44% | 1,861,653 | $105.1M | Add +15.4% |
| LEGN Legend Biotech Corp.-ADR | 0.44% | 5,763,475 | $104.3M | Reduce -6.5% |
| KEY Keycorp | 0.44% | 5,193,334 | $104.1M | Add +28.5% |
| ROST Ross Stores Inc. | 0.43% | 471,916 | $102.2M | New |
| PLMR Palomar Holdings Inc. | 0.43% | 854,116 | $102.1M | Add +1.6% |
| PANW Palo Alto Networks Inc. | 0.43% | 636,483 | $102.0M | Add +41.9% |
| FANG Diamondback Energy Inc. | 0.42% | 503,474 | $99.6M | Add +42.0% |
| PLTR Palantir Technologies Inc. Class A | 0.41% | 674,557 | $98.7M | Add +336.4% |
| SMTC Semtech Corp. | 0.41% | 1,280,594 | $98.5M | Reduce -47.7% |
| WWD Woodward Inc. | 0.41% | 272,185 | $97.4M | New |
| ANET Arista Networks Inc. | 0.40% | 780,402 | $95.8M | New |
| AZO AutoZone Inc. | 0.40% | 28,363 | $95.8M | Reduce -44.5% |
| SN Sharkninja Inc. | 0.40% | 904,541 | $95.8M | Add +7.7% |
| COHR Coherent Corp. | 0.40% | 396,644 | $94.5M | Reduce -40.4% |
| ALAB Astera Labs Inc. | 0.40% | 860,113 | $94.3M | Add +340.4% |
| BRZE Braze Inc. Class A | 0.39% | 3,973,906 | $93.8M | Add +81.7% |
| JBL Jabil Inc. | 0.39% | 349,209 | $92.8M | Add +6.3% |
| LECO Lincoln Electric Holdings | 0.37% | 358,165 | $89.2M | Add +6.0% |
| IMAX Imax Corp. | 0.37% | 2,338,776 | $88.9M | Reduce -0.3% |
| WGS Genedx Holdings Corp. | 0.37% | 1,369,108 | $87.9M | Add +34.5% |
| GRMN Garmin Ltd. | 0.37% | 376,362 | $87.3M | Add +12.1% |
| CRDO Credo Technology Group Holdi | 0.36% | 926,219 | $86.9M | Add +96.8% |
| FFIV F5 Inc. | 0.36% | 298,542 | $86.4M | Add +6.1% |
| EWBC East West Bancorp Inc. | 0.36% | 805,956 | $86.0M | Reduce -7.8% |
| LTH Life Time Group Holdings Inc. | 0.36% | 3,185,515 | $85.8M | New |
| BIRK Birkenstock Holding PLC | 0.35% | 2,338,779 | $83.8M | Add +19.6% |
| ORLY O'reilly Automotive Inc. | 0.34% | 887,999 | $82.0M | Reduce -6.8% |
| MS Morgan Stanley | 0.34% | 496,558 | $81.7M | New |
| XENE Xenon Pharmaceuticals Inc. | 0.34% | 1,401,483 | $81.5M | Add +14.2% |
| ALNY Alnylam Pharmaceuticals Inc. | 0.34% | 245,539 | $81.2M | Add +162.8% |
| FCFS Firstcash Holdings Inc. | 0.34% | 431,993 | $81.2M | Reduce -19.7% |
| IEX Idex Corp. | 0.34% | 426,019 | $80.8M | Add +6.0% |
| MTZ Mastec Inc. | 0.34% | 249,980 | $80.4M | New |
| HLI Houlihan Lokey Inc. | 0.33% | 543,611 | $78.1M | Add +4.5% |
| PLXS Plexus Corp. | 0.33% | 384,493 | $77.9M | Add +7294.1% |
Portfolio Sells Q4 2025 → Q1 2026
| BAC Bank of America Corp. | Reduce -72.1% | 0.22% | −0.66 |
| MASI Masimo Corp. | Reduce -77.6% | 0.25% | −0.57 |
| CVLT Commvault Systems Inc. | Sold out | 0.00% | −0.55 |
| TEAM Atlassian Corp. Class A | Sold out | 0.00% | −0.55 |
| META Meta Platforms Inc. Class A | Reduce -19.6% | 1.26% | −0.54 |
| ADMA Adma Biologics Inc. | Sold out | 0.00% | −0.53 |
| HQY Healthequity Inc. | Reduce -63.5% | 0.25% | −0.50 |
| PODD Insulet Corp. | Reduce -99.6% | 0.00% | −0.46 |
| HEI.A Heico Corp. Class A | Reduce -95.1% | 0.02% | −0.42 |
| CWST Casella Waste Systems Inc. Class A | Reduce -50.6% | 0.27% | −0.41 |
| ALKT Alkami Technology Inc. | Sold out | 0.00% | −0.40 |
| GOOGL Alphabet Inc. Class A | Reduce -7.0% | 2.45% | −0.40 |
| DXCM Dexcom Inc. | Reduce -98.1% | 0.01% | −0.39 |
| ABBV Abbvie Inc. | Reduce -97.5% | 0.01% | −0.39 |
| ORCL Oracle Corp. | Sold out | 0.00% | −0.39 |
| AAPL Apple Inc. | Reduce -4.3% | 3.34% | −0.37 |
| TSLA Tesla Inc. | Reduce -31.5% | 0.49% | −0.37 |
| BURL Burlington Stores Inc. | Sold out | 0.00% | −0.36 |
| HUBS HubSpot Inc. | Reduce -33.8% | 0.24% | −0.35 |
| DKNG Draftkings Inc. Class A | Sold out | 0.00% | −0.34 |
| SMTC Semtech Corp. | Reduce -47.7% | 0.41% | −0.34 |
| TRU Transunion | Sold out | 0.00% | −0.33 |
| NOW ServiceNow Inc. | Reduce -5.6% | 0.61% | −0.33 |
| AZO AutoZone Inc. | Reduce -44.5% | 0.40% | −0.32 |
| UNH Unitedhealth Group Inc. | Reduce -98.8% | 0.00% | −0.31 |
| RVMD Revolution Medicines Inc. | Reduce -45.3% | 0.64% | −0.31 |
| V Visa Inc. Class A | Reduce -24.4% | 0.58% | −0.30 |
| VMC Vulcan Materials Co. | Sold out | 0.00% | −0.30 |
| SLAB Silicon Laboratories Inc. | Sold out | 0.00% | −0.30 |
| AJG Arthur J Gallagher & Co. | Sold out | 0.00% | −0.28 |
| OWL Blue Owl Capital Inc. | Sold out | 0.00% | −0.28 |
| GENI Genius Sports Ltd. | Reduce -96.5% | 0.00% | −0.27 |
| FITB Fifth Third Bancorp | Reduce -36.3% | 0.47% | −0.27 |
| PRI Primerica Inc. | Sold out | 0.00% | −0.25 |
| AMZN Amazon.com Inc. | Reduce -2.2% | 1.99% | −0.25 |
| IRTC Irhythm Holdings Inc. | Sold out | 0.00% | −0.24 |
| OPCH Option Care Health Inc. | Reduce -57.2% | 0.13% | −0.23 |
| WCN Waste Connections Inc. | Reduce -98.6% | 0.00% | −0.23 |
| BLD Topbuild Corp. | Reduce -41.8% | 0.22% | −0.23 |
| AMD Advanced Micro Devices | Reduce -98.0% | 0.00% | −0.22 |
| DHR Danaher Corp. | Reduce -65.6% | 0.09% | −0.22 |
| BIO Bio-Rad Laboratories-A | Sold out | 0.00% | −0.21 |
| FNB FNB Corp. | Sold out | 0.00% | −0.21 |
| BLDR Builders Firstsource Inc. | Sold out | 0.00% | −0.20 |
| DSGX The Descartes Systems Grp | Reduce -32.8% | 0.24% | −0.20 |
| RYAN Ryan Specialty Holdings Inc. | Sold out | 0.00% | −0.18 |
| NIQ Niq Global Intelligence PLC | Sold out | 0.00% | −0.16 |
| TT Trane Technologies PLC | Reduce -86.6% | 0.03% | −0.16 |
| RBLX Roblox Corp. Class A | Sold out | 0.00% | −0.16 |
| RNAM Avidity Biosciences Inc. | Sold out | 0.00% | −0.14 |
Portfolio Buys Q4 2025 → Q1 2026
| FTAI Ftai Aviation Ltd. | Add +21.2% | 2.93% | +1.00 |
| INSM Insmed Inc. | Add +239.5% | 1.01% | +0.69 |
| LNG Cheniere Energy Inc. | New | 0.55% | +0.55 |
| AS Amer Sports Inc. | New | 0.54% | +0.54 |
| AIG American International Group | New | 0.46% | +0.46 |
| MKSI MKS Inc. | Add +24.6% | 1.01% | +0.45 |
| JLL Jones Lang Lasalle Inc. | New | 0.44% | +0.44 |
| ROST Ross Stores Inc. | New | 0.43% | +0.43 |
| WWD Woodward Inc. | New | 0.41% | +0.41 |
| ANET Arista Networks Inc. | New | 0.40% | +0.40 |
| LTH Life Time Group Holdings Inc. | New | 0.36% | +0.36 |
| MS Morgan Stanley | New | 0.34% | +0.34 |
| MTZ Mastec Inc. | New | 0.34% | +0.34 |
| PLXS Plexus Corp. | Add +7294.1% | 0.33% | +0.32 |
| PR Permian Resources Corp. Class A | Add +25.7% | 0.67% | +0.32 |
| HWM Howmet Aerospace Inc. | Add +3.2% | 2.21% | +0.32 |
| GWRE Guidewire Software Inc. | New | 0.31% | +0.31 |
| PLTR Palantir Technologies Inc. Class A | Add +336.4% | 0.41% | +0.30 |
| GH Guardant Health Inc. | Add +152.7% | 0.53% | +0.30 |
| LOW Lowe's Cos Inc. | New | 0.30% | +0.30 |
| NAMS Newamsterdam Pharma Co. NV | New | 0.30% | +0.30 |
| PWR Quanta Services Inc. | Add +21.3% | 0.76% | +0.28 |
| CELH Celsius Holdings Inc. | Add +144.1% | 0.56% | +0.27 |
| MCHP Microchip Technology Inc. | New | 0.26% | +0.26 |
| BE Bloom Energy Corp. Class A | Add +4.0% | 0.68% | +0.26 |
| FN Fabrinet | Add +49.8% | 0.62% | +0.26 |
| ALAB Astera Labs Inc. | Add +340.4% | 0.40% | +0.26 |
| GEV GE Vernova Inc. | Add +12.0% | 0.73% | +0.25 |
| APG Api Group Corp. | Add +34.2% | 0.79% | +0.24 |
| IBP Installed Building Products | New | 0.23% | +0.23 |
| FTI Technipfmc PLC | Add +4.2% | 0.59% | +0.23 |
| GKOS Glaukos Corp. | New | 0.22% | +0.22 |
| CDE Coeur Mining Inc. | New | 0.22% | +0.22 |
| MAR Marriott International Class A | New | 0.21% | +0.21 |
| PCVX Vaxcyte Inc. | Add +3.0% | 0.89% | +0.21 |
| MDGL Madrigal Pharmaceuticals Inc. | New | 0.21% | +0.21 |
| NXPI NXP Semiconductors NV | New | 0.20% | +0.20 |
| FANG Diamondback Energy Inc. | Add +42.0% | 0.42% | +0.20 |
| PL Planet Labs PBC | New | 0.19% | +0.19 |
| ALNY Alnylam Pharmaceuticals Inc. | Add +162.8% | 0.34% | +0.19 |
| TPR Tapestry Inc. | Add +4.8% | 1.30% | +0.19 |
| ENTG Entegris Inc. | New | 0.18% | +0.18 |
| LPLA LPL Financial Holdings Inc. | Add +40.9% | 1.11% | +0.18 |
| RIOT Riot Platforms Inc. | New | 0.18% | +0.18 |
| CPAY Corpay Inc. | New | 0.17% | +0.17 |
| NFLX Netflix Inc. | Add +23.3% | 0.79% | +0.17 |
| TRGP Targa Resources Corp. | Add +53.6% | 0.32% | +0.17 |
| NXT Nextpower Inc. | Add +1.6% | 0.56% | +0.16 |
| LLY Eli Lilly & Co. | Add +31.4% | 1.41% | +0.16 |
| HLT Hilton Worldwide Holdings Inc. | Add +27.9% | 0.58% | +0.16 |
All Filings
| Quarter | Positions | 13F Reported Value | Top Holdings |
|---|---|---|---|
| Q2 2026 | 278 | $30.6B | NVDA, GOOGL, ASND, AXON, FTAI |
| Q1 2026 | 250 | $23.8B | NVDA, ASND, FIX, AAPL, FTAI |
| Q4 2025 | 241 | $24.0B | NVDA, ASND, AAPL, MSFT, GOOGL |
| Q3 2025 | 235 | $23.8B | NVDA, ASND, MSFT, AAPL, FIX |
| Q2 2025 | 239 | $23.8B | NVDA, ASND, MSFT, AAPL, AMZN |
| Q1 2025 | 244 | $20.5B | ASND, NVDA, AAPL, MSFT, AMZN |
| Q4 2024 | 239 | $23.0B | NVDA, AAPL, MSFT, ASND, AMZN |
| Q3 2024 | 247 | $22.1B | NVDA, AAPL, MSFT, ASND, AMZN |
| Q2 2024 | 248 | $20.4B | NVDA, MSFT, AAPL, ASND, AMZN |
| Q1 2024 | 244 | $19.0B | MSFT, ASND, AAPL, NVDA, AMZN |