Who owns Castle Biosciences, Inc. (CSTL)
Which tracked institutional funds hold CSTL, how they are positioned, and who is buying versus exiting — from SEC Form 13F-HR filings. See CSTL company fundamentals →
Ownership as of the 2026-Q1 13F filings (latest filed 2026-05-18). 13F is disclosed up to 45 days after quarter-end, so the most recent quarter fills in over the following weeks.
How the tape is positioned
The tracked-fund tape on CSTL is one-sided between 2025-Q4 and 2026-Q1: 22 added or opened and 80 trimmed or exited — on balance reducing.
A prompt to read the filings, not a verdict. 13F is a quarter-end snapshot disclosed up to 45 days late; a fund adds or exits for mandate, benchmark, and timing reasons that have nothing to do with a view on the stock. This is a starting question, not a signal to trade.
Conviction spread
CSTL’s largest tracked holder by dollar value, VANGUARD GROUP INC, sizes it at 0.0% of its own reported 13F book, while the median holder sizes it at 0.0% of theirs — a 0.0pp gap the other way — the median holder sizes CSTL more heavily than its largest holder by dollar value does.
Book-share is each fund’s reported value in CSTL divided by its whole reported 13F book, so it is comparable across funds of different sizes and is unaffected by stock splits. A higher share means a fund has committed more of its book to the name — a starting question about conviction, not a verdict or a signal to trade.
Institutional & insider positioning
Between 2025-Q4 and 2026-Q1, across 187 tracked filers holding CSTL, 102 increased or opened the position and 99 reduced or closed it; over the same quarter, open-market insider Form 4 buying and selling roughly offset.
This fuses two public signals for the same quarter — how tracked institutions changed their positions and whether insiders bought or sold in the open market. It describes what was filed; it is a starting question, not a verdict or a signal to trade.
New buyers & exits
Funds opening or closing a position in CSTL between the 2025-Q4 and 2026-Q1 13F filings, and the largest changes among funds holding it in both. New buyers and exits are counted on fund presence (split-invariant); adds and trims are measured on reported value.
New buyers 10
- VANGUARD CAPITAL MANAGEMENT LLC$29M
- VANGUARD PORTFOLIO MANAGEMENT LLC$21M
- VANGUARD FIDUCIARY TRUST CO$5M
- Campbell & CO Investment Adviser LLC$4M
- FORMULA GROWTH LTD$1M
- KBC Group NV$907K
Full exits 13
- VANGUARD GROUP INC$77M
- WELLINGTON MANAGEMENT GROUP LLP$9M
- BRAIDWELL LP$7M
- Point72 Asset Management, L.P.$5M
- Informed Momentum Co LLC$3M
- Squarepoint Ops LLC$2M
Largest adds
- SG Americas Securities, LLC$5M
- Qube Research & Technologies Ltd$5M
- PANAGORA ASSET MANAGEMENT INC$4M
- TWO SIGMA INVESTMENTS, LP$3M
- MORGAN STANLEY$3M
- SummitTX Capital, L.P.$968K
Largest trims
- BlackRock, Inc.$48M
- Portolan Capital Management, LLC$34M
- PRINCIPAL FINANCIAL GROUP INC$27M
- DIMENSIONAL FUND ADVISORS LP$19M
- SUMMIT PARTNERS PUBLIC ASSET MANAGEMENT, LLC$18M
- RTW INVESTMENTS, LP$15M
Institutional holders
One row per tracked fund, largest reported value first. “% of value” is the fund’s share of this security’s tracked institutional value — not of shares outstanding. Rows marked stale are from an earlier filing than the security’s latest quarter — that fund is absent from the newest snapshot (position exited, or reported under a different name).
| Fund | Shares | Reported value | % of value | Quarter |
|---|---|---|---|---|
| BlackRock, Inc. trimmed | 2,982,946 | $73M | 9.2% | 2026-Q1 |
| RTW INVESTMENTS, LP added | 2,758,335 | $68M | 8.5% | 2026-Q1 |
| PRINCIPAL FINANCIAL GROUP INC trimmed | 1,769,877 | $43M | 5.4% | 2026-Q1 |
| Portolan Capital Management, LLC trimmed | 1,350,283 | $33M | 4.2% | 2026-Q1 |
| VANGUARD CAPITAL MANAGEMENT LLC new | 1,177,522 | $29M | 3.6% | 2026-Q1 |
| DIMENSIONAL FUND ADVISORS LP trimmed | 1,039,761 | $26M | 3.2% | 2026-Q1 |
| SUMMIT PARTNERS PUBLIC ASSET MANAGEMENT, LLC trimmed | 940,685 | $23M | 2.9% | 2026-Q1 |
| VANGUARD PORTFOLIO MANAGEMENT LLC new | 861,771 | $21M | 2.7% | 2026-Q1 |
| Allianz Asset Management GmbH added | 811,324 | $20M | 2.5% | 2026-Q1 |
| STATE STREET CORP added | 769,079 | $19M | 2.4% | 2026-Q1 |
| GEODE CAPITAL MANAGEMENT, LLC added | 728,100 | $18M | 2.2% | 2026-Q1 |
| AIGH Capital Management LLC trimmed | 590,601 | $14M | 1.8% | 2026-Q1 |
| Qube Research & Technologies Ltd added | 559,583 | $14M | 1.7% | 2026-Q1 |
| PALISADE CAPITAL MANAGEMENT, LP trimmed | 535,884 | $13M | 1.6% | 2026-Q1 |
| RENAISSANCE TECHNOLOGIES LLC added | 532,800 | $13M | 1.6% | 2026-Q1 |
| Nuveen, LLC trimmed | 522,127 | $13M | 1.6% | 2026-Q1 |
| ACADIAN ASSET MANAGEMENT LLC added | 484,441 | $12M | 1.5% | 2026-Q1 |
| WASATCH ADVISORS LP trimmed | 455,036 | $11M | 1.4% | 2026-Q1 |
| MORGAN STANLEY added | 428,934 | $11M | 1.3% | 2026-Q1 |
| EVENTIDE ASSET MANAGEMENT, LLC added | 386,425 | $9M | 1.2% | 2026-Q1 |
| Connor, Clark & Lunn Investment Management Ltd. trimmed | 377,082 | $9M | 1.2% | 2026-Q1 |
| MILLENNIUM MANAGEMENT LLC added | 353,319 | $9M | 1.1% | 2026-Q1 |
| GOLDMAN SACHS GROUP INC added | 341,171 | $8M | 1.0% | 2026-Q1 |
| SCHRODER INVESTMENT MANAGEMENT GROUP trimmed | 298,941 | $7M | 0.9% | 2026-Q1 |
| NORTHERN TRUST CORP added | 273,101 | $7M | 0.8% | 2026-Q1 |
| SILVERCREST ASSET MANAGEMENT GROUP LLC added | 268,535 | $7M | 0.8% | 2026-Q1 |
| KORNITZER CAPITAL MANAGEMENT INC /KS trimmed | 264,396 | $6M | 0.8% | 2026-Q1 |
| BRIDGEWAY CAPITAL MANAGEMENT, LLC added | 255,184 | $6M | 0.8% | 2026-Q1 |
| TWO SIGMA INVESTMENTS, LP added | 248,840 | $6M | 0.8% | 2026-Q1 |
| Advisors Capital Management, LLC trimmed | 248,376 | $6M | 0.8% | 2026-Q1 |
| SG Americas Securities, LLC added | 244,886 | $6M | 0.8% | 2026-Q1 |
| CHARLES SCHWAB INVESTMENT MANAGEMENT INC trimmed | 241,880 | $6M | 0.7% | 2026-Q1 |
| NEW YORK STATE COMMON RETIREMENT FUND | 233,046 | $6M | 0.7% | 2026-Q1 |
| TUDOR INVESTMENT CORP ET AL added | 222,982 | $5M | 0.7% | 2026-Q1 |
| PANAGORA ASSET MANAGEMENT INC added | 222,353 | $5M | 0.7% | 2026-Q1 |
| D. E. Shaw & Co., Inc. added | 211,966 | $5M | 0.7% | 2026-Q1 |
| VANGUARD FIDUCIARY TRUST CO new | 188,211 | $5M | 0.6% | 2026-Q1 |
| Allspring Global Investments Holdings, LLC added | 160,663 | $4M | 0.5% | 2026-Q1 |
| Campbell & CO Investment Adviser LLC added | 148,824 | $4M | 0.5% | 2026-Q1 |
| Empowered Funds, LLC added | 132,184 | $3M | 0.4% | 2026-Q1 |
| Trexquant Investment LP added | 130,434 | $3M | 0.4% | 2026-Q1 |
| Parkman Healthcare Partners LLC trimmed | 126,150 | $3M | 0.4% | 2026-Q1 |
| BNP PARIBAS FINANCIAL MARKETS trimmed | 122,156 | $3M | 0.4% | 2026-Q1 |
| CITADEL ADVISORS LLC trimmed | 120,977 | $3M | 0.4% | 2026-Q1 |
| FRANKLIN RESOURCES INC added | 90,909 | $2M | 0.3% | 2026-Q1 |
| Bank of New York Mellon Corp added | 88,654 | $2M | 0.3% | 2026-Q1 |
| JPMORGAN CHASE & CO trimmed | 88,771 | $2M | 0.3% | 2026-Q1 |
| AMERICAN CENTURY COMPANIES INC added | 79,107 | $2M | 0.2% | 2026-Q1 |
| Orion Porfolio Solutions, LLC added | 74,896 | $2M | 0.2% | 2026-Q1 |
| MACKENZIE FINANCIAL CORP added | 74,111 | $2M | 0.2% | 2026-Q1 |
| BANK OF AMERICA CORP /DE/ trimmed | 67,810 | $2M | 0.2% | 2026-Q1 |
| SummitTX Capital, L.P. added | 67,033 | $2M | 0.2% | 2026-Q1 |
| UBS AM, a distinct business unit of UBS ASSET MANAGEMENT AMERICAS LLC trimmed | 64,964 | $2M | 0.2% | 2026-Q1 |
| AQR CAPITAL MANAGEMENT LLC trimmed | 63,386 | $2M | 0.2% | 2026-Q1 |
| ENVESTNET ASSET MANAGEMENT INC trimmed | 61,865 | $2M | 0.2% | 2026-Q1 |
| Invesco Ltd. trimmed | 61,012 | $1M | 0.2% | 2026-Q1 |
| Swiss National Bank | 57,300 | $1M | 0.2% | 2026-Q1 |
| FMR LLC added | 50,412 | $1M | 0.2% | 2026-Q1 |
| UBS Group AG trimmed | 49,163 | $1M | 0.2% | 2026-Q1 |
| Man Group plc added | 47,138 | $1M | 0.1% | 2026-Q1 |
| FORMULA GROWTH LTD new | 46,000 | $1M | 0.1% | 2026-Q1 |
| Quantinno Capital Management LP added | 45,476 | $1M | 0.1% | 2026-Q1 |
| JANE STREET GROUP, LLC trimmed | 42,562 | $1M | 0.1% | 2026-Q1 |
| Schonfeld Strategic Advisors LLC added | 42,413 | $1M | 0.1% | 2026-Q1 |
| ALLIANCEBERNSTEIN L.P. | 25,270 | $983K | 0.1% | 2026-Q1 |
| RHUMBLINE ADVISERS trimmed | 38,378 | $942K | 0.1% | 2026-Q1 |
| PRICE T ROWE ASSOCIATES INC /MD/ added | 37,792 | $928K | 0.1% | 2026-Q1 |
| KBC Group NV new | 36,932 | $907K | 0.1% | 2026-Q1 |
| NOMURA HOLDINGS INC new | 35,748 | $878K | 0.1% | 2026-Q1 |
| SEI INVESTMENTS CO trimmed | 35,046 | $860K | 0.1% | 2026-Q1 |
| ALGERT GLOBAL LLC added | 34,778 | $854K | 0.1% | 2026-Q1 |
| Universal- Beteiligungs- und Servicegesellschaft mbH added | 34,387 | $844K | 0.1% | 2026-Q1 |
| ExodusPoint Capital Management, LP trimmed | 32,608 | $801K | 0.1% | 2026-Q1 |
| Corient Private Wealth LLC new | 31,870 | $782K | 0.1% | 2026-Q1 |
| CALIFORNIA STATE TEACHERS RETIREMENT SYSTEM trimmed | 27,513 | $675K | 0.1% | 2026-Q1 |
| ARROWSTREET CAPITAL, LIMITED PARTNERSHIP added | 27,142 | $666K | 0.1% | 2026-Q1 |
| BARCLAYS PLC trimmed | 26,810 | $658K | 0.1% | 2026-Q1 |
| VANGUARD GROUP INC trimmed | 1,979,313 | $77M | 9.7% | 2025-Q4 stale |
| Park West Asset Management LLC new | 556,485 | $11M | 1.4% | 2025-Q1 stale |
| WELLINGTON MANAGEMENT GROUP LLP trimmed | 218,560 | $9M | 1.1% | 2025-Q4 stale |
| BRAIDWELL LP trimmed | 177,183 | $7M | 0.9% | 2025-Q4 stale |
| Bellevue Group AG trimmed | 301,103 | $6M | 0.8% | 2025-Q1 stale |
| Point72 Asset Management, L.P. trimmed | 119,458 | $5M | 0.6% | 2025-Q4 stale |
| SUMMIT WEALTH GROUP LLC / CO new | 122,494 | $5M | 0.6% | 2025-Q3 stale |
| SHELTON CAPITAL MANAGEMENT | 164,008 | $3M | 0.4% | 2025-Q1 stale |
| Informed Momentum Co LLC added | 74,138 | $3M | 0.4% | 2025-Q4 stale |
| Squarepoint Ops LLC trimmed | 55,118 | $2M | 0.3% | 2025-Q4 stale |
| Orion Portfolio Solutions, LLC added | 78,409 | $2M | 0.2% | 2025-Q1 stale |
| AMERIPRISE FINANCIAL INC trimmed | 35,368 | $1M | 0.2% | 2025-Q4 stale |
| TWO SIGMA ADVISERS, LP added | 29,899 | $1M | 0.1% | 2025-Q4 stale |
| Cubist Systematic Strategies, LLC trimmed | 50,304 | $1M | 0.1% | 2025-Q3 stale |
| DARK FOREST CAPITAL MANAGEMENT LP added | 51,855 | $1M | 0.1% | 2025-Q1 stale |
| TRITONPOINT WEALTH, LLC | 40,777 | $928K | 0.1% | 2025-Q3 stale |
| Nebula Research & Development LLC added | 44,472 | $908K | 0.1% | 2025-Q2 stale |
| CAXTON ASSOCIATES LLP added | 22,464 | $874K | 0.1% | 2025-Q4 stale |
| HEALTHCARE OF ONTARIO PENSION PLAN TRUST FUND | 35,800 | $815K | 0.1% | 2025-Q3 stale |
| HSBC HOLDINGS PLC trimmed | 19,486 | $760K | 0.1% | 2025-Q4 stale |
| ABG Innovation Capital Partners III GP Ltd | 36,747 | $736K | 0.1% | 2025-Q1 stale |
| AlphaQuest LLC added | 17,116 | $666K | 0.1% | 2025-Q4 stale |
| Verition Fund Management LLC added | 16,811 | $654K | 0.1% | 2025-Q4 stale |
Ownership over time
Tracked institutional holder count and total shares held by filing quarter (independent scales). The curated-era tail and any mid-ingest latest quarter are handled honestly — a partial quarter is not drawn as a collapse.
Reading this table
Funds hold the same stock for different reasons — an index fund “holds” almost everything, an active manager sizes a name to a mandate and a benchmark, and each fund entered at its own price and time. Because 13F is filed up to 45 days after quarter-end, every row is a backward-looking snapshot; a manager may have traded since. Share-class siblings (a company’s A and C shares) are rolled up to one line so a dual-class name is never double-counted. Compare like-for-like. A large holder is not an endorsement, and a fund exiting is not a warning — this is a starting question, not a verdict.
About 13F filings
A Form 13F is a quarterly disclosure that institutional investment managers with over $100 million in US-listed equities must file with the SEC. In plain English: it is a snapshot of the long stock positions a fund held at the end of a quarter. It covers long US-listed equities only — not short positions, options, cash, or private holdings — and the funds shown are the large sample we track, not the complete 13F universe.