WESTFIELD CAPITAL MANAGEMENT CO LP
SEC Form 13F institutional filer · CIK 0001177719
13F-HR · 123 reported holdings · 2026-03-31
Westfield Capital Management Co LP is an asset manager.
Reported long-US-equity value
$13.86B
Top-10 concentration
50.4%
WESTFIELD CAPITAL MANAGEMENT CO LP — $13.9B AUM allocation strategy
WESTFIELD CAPITAL MANAGEMENT CO LP files SEC Form 13F and reports $13.9B of long US equity value across 123 reported holdings for 2026-03-31.
Its largest sector bet is Information Technology 22.1%, followed by Industrials 20.5% and Financials 9.2%.
The top 10 holdings account for 50% of reported value — a conviction-weighted book concentrated in its best ideas. The sector and industry splits below are of the same reported value. Track quarter-over-quarter adds, trims, new positions and exits below — sourced from SEC 13F filings, public domain.
WESTFIELD CAPITAL MANAGEMENT CO LP — latest SEC 13F insights
Reported long-US-equity value (13F AUM)
$13.9B
total across 123 reported holdings · 2026-03-31 · excludes shorts, cash, non-US
Top-10 concentration
50% of value
higher = narrower conviction; lower = spread / hedging
Biggest adds (shares)
+$KEY +1.15M sh · +$20.7M+$PLTR +520K sh · +$71.2M+$ARES +422K sh · −$14.5M
Biggest trims (shares)
−$BAC −2.76M sh · −$158M−$DXCM −1.41M sh · −$93.9M−$FITB −1.36M sh · −$64.6M
Exited to nil (held last quarter, gone now)
$ORCL ($92.5M last qtr)$VMC ($72.5M last qtr)$AJG ($67.2M last qtr)$BLDR ($48.9M last qtr)$IVV ($11.2M last qtr)
Sector allocation (share of reported value)
each slice is a share of the reported long-US-equity value — smaller sectors and the rest of the book roll into “Other holdings”
Qtr shift = share-point change vs the prior quarter's filing — first period tracked for this filer; the column fills in with the next quarterly refresh.
Industry allocation (share of reported value)
- Semiconductors11.9%—
- Asset Management & Custody Banks9.2%—
- Construction & Engineering7.5%—
- Aerospace & Defense7.1%—
- Interactive Media & Services6.4%—
- Technology Hardware, Storage & Peripherals5.7%—
- Electrical Components & Equipment4.7%—
- Systems Software4.4%—
- Other holdings43.1%—
the finer GICS cut of the same book — same denominator — smaller industries roll into “Other holdings”
Qtr shift = share-point change vs the prior quarter's filing — first period tracked for this filer; the column fills in with the next quarterly refresh.
Top S&P 500 holdings
10 of 10 rows · sorted by Value ↓
| Ticker | Holding | Shares | Value | Δ QoQ | Weight |
|---|---|---|---|---|---|
| $NVDA | NVIDIA Corporation | 6.32M | $1.1B | +366K | 8.0% |
| $BNY | The Bank of New York Mellon Corporation | 4.81M | $1.1B | -372K | 7.9% |
| $FIX | Comfort Systems USA Inc | 621K | $856M | -47.9K | 6.2% |
| $AAPL | Apple Inc | 3.13M | $795M | -141K | 5.7% |
| $MSFT | Microsoft Corporation | 1.65M | $611M | +28.3K | 4.4% |
| $GOOG | Alphabet Inc. Class C Capital Stock | 2.03M | $583M | -152K | 4.2% |
| $HWM | Howmet Aerospace Inc | 2.29M | $528M | +70.6K | 3.8% |
| $VRT | Vertiv Holdings LLC | 1.92M | $482M | -356K | 3.5% |
| $AMZN | Amazon.com Inc | 2.28M | $475M | -51.1K | 3.4% |
| $AXON | Axon Enterprise Inc | 1.06M | $452M | +233K | 3.3% |
…and 113 more holdings in the full 13F filing (top positions only shown).
SEC Form 13F data sets · public domain · 45-day filing lag · >$100M AUM managers · as reported
← All 13F filers·← QuantOrb.pro
How to read Δ QoQ — the five insight categories, and the caveats
The categories. Analysts, quants and retail traders look past total portfolio value to isolate actionable signals. Five categories matter.
Conviction & concentration shifts
New positions vs complete exits — a brand-new stock signals high conviction; a full liquidation suggests a broken thesis or tax-loss harvesting. Aggressive sizing — look at share count, not dollars: a 20% share increase during a drawdown is strong dip-buying. Concentration — a narrowing top-5/10 means conviction; spreading capital across more names means hedging.
Sector & macro allocation rotations
Aggregating Δ QoQ moves across sectors shows where smart money is leaning in or sneaking out — rotating out of growth into defensives or energy, for example. The fund's total long equity exposure quarter-over-quarter is a proxy for overall institutional risk appetite.
Crowding & smart-money consensus
When several managers initiate or expand the same stock in the same quarter, that is institutional consensus. Contrarian reads: top pickers buying hard into a beaten-down name the market is selling.
Derivative & option overlays
Reported call/put changes indicate whether managers are adding downside hedges or leveraging upside exposure. Note: a long increase may be half of a market-neutral pair trade.
Who reads this
| Retail "cloners" | High-conviction ideas to replicate ~45 days after quarter-end. |
| Corporate IR | Which funds bought or dumped the stock, before the next call. |
| Quant / algo traders | Cross-sectional factor inputs: flow, momentum, ownership. |
Four caveats before you trade on it
- 45-day lag — holdings are quarter-end; positions may already be closed.
- Long-only — 13Fs miss shorts, pair trades and cash.
- No non-US / fixed income — the picture is US equities plus options.
- Corporate actions — splits and spinoffs distort raw share deltas.
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