WILLIAM BLAIR INVESTMENT MANAGEMENT, LLC
"13F equity value" = market value of this filer's US-listed long equity positions only. It excludes cash, bonds, non-US and short positions, so it understates a fund's true assets under management — often by a lot.
13F holdings are disclosed ~45 days after quarter-end, and they never reveal when within the quarter a fund actually bought. So any 13F-based summary is structurally late and blurred — this applies to every fund, including this one.
We backtested copying it anyway. Buying this fund's new positions the day each filing went public, over 32 quarters, returned +2.9% per quarter — versus +2.7% per quarter from simply owning every 13F stock. It beat that baseline in only 50.0% of quarters (excess t = 1.67, not statistically significant). Its filings tell you what it bought — not what you should buy.
Quarterly compounding, invested quarters only · entry 47 days after quarter-end (when 13F data becomes public)
Top 20 holdings of 413 · 2026 Q1
| Ticker | Value | Weight | QoQ |
|---|---|---|---|
| TSM | $1.9B | | TRIM |
| NVDA | $1.6B | | TRIM |
| AAPL | $1.2B | | TRIM |
| MSFT | $1.1B | | TRIM |
| GOOGL | $720M | | TRIM |
| AVGO | $681M | | TRIM |
| AMZN | $659M | | TRIM |
| META | $580M | | TRIM |
| MA | $530M | | TRIM |
| AZN | $377M | | NEW |
| LIN | $315M | | HOLD |
| CG | $305M | | TRIM |
| COST | $301M | | TRIM |
| ITUB | $266M | | TRIM |
| TWST | $250M | | TRIM |
| NOW | $248M | | ADD |
| PRMB | $246M | | ADD |
| MLI | $234M | | ADD |
| INTU | $231M | | ADD |
| MNST | $213M | | TRIM |
QoQ vs previous quarter's share count · NEW = new position · ADD/TRIM = ±2% shares · HOLD = unchanged.
New positions in 2026 Q1
Method & Limitations
Method: a "new position" = held this quarter, absent last quarter (options excluded; stocks with <50 prior holders excluded to filter spin-off artifacts). Entry 47 days after quarter-end — the first day the public could act on the filing. Benchmark = equal-weighted universe of all 13F-held stocks. Limitations: quarterly snapshots can't see intra-quarter trades; survivorship bias — funds that shut down are absent, which flatters the sample. Statistics, not advice.