SEC Form 4
Crescent Biopharma, Inc. (CBIO) insider trading
In the 12 months to Oct 26, 2026, one CBIO insider reported open-market purchases of $30.6M across 2 filings; no open-market sales were filed.
Latest filing · Last 12 months · Source: SEC EDGAR · How we count
- Open-market sales
- $0
- 0 filings · 0 insiders
- Open-market purchases
- $30.6M
- 2 filings · Tomas Kiselak, Director
Who traded CBIO, and when
- Purchase
CBIO daily close from Oct 27, 2025 to Oct 26, 2026, between $8.94 and $26.98, last $12.60. 0 sale and 2 purchase filings by 1 insider, marked at their filing dates. Tomas Kiselak, Director: bought $30.6M across 2 filings, first filed Dec 8, 2025, last Jul 20, 2026.
Largest mark · tap a row for others
Tomas Kiselak · Director
Purchase $18,237,600
1,360,000 shares
Filed Dec 8, 2025 · traded Dec 4
Close on filing date $13.17
Tomas Kiselak · Director
Director
$30.6M boughtOpen-market trades
2 filings in the last 12 months| Insider | Role | Sold | Bought | Filings | Pre-arranged (10b5-1) | Last filed |
|---|---|---|---|---|---|---|
| Tomas Kiselak | Director | — | $30.6M | 2 | — |
| Filed | Insider | Type | Shares | Value | Held after | Source |
|---|---|---|---|---|---|---|
traded | Tomas Kiselak Director | Purchase | 853,450 ordinary shares | $12.4M | 3,601,316 | |
traded | Tomas Kiselak Director | Purchase | 1,360,000 ordinary shares | $18.2M | 2,747,866 |
Shares are as filed (ordinary shares or ADS); values are as converted to US$ in the filing.
GET /stocks/filings/vX/form-4?tickers=CBIO&filing_date.gte=2025-10-26&sort=filing_date.desc&limit=500{
"status": "OK",
"results": [
{
"tickers": [
"CBIO",
"GLYC"
],
"issuer_cik": "0001253689",
"owner_cik": "0001830177",
"accession_number": "0001104659-26-085113",
"form_type": "4",
"filing_date": "2026-07-20",
"period_of_report": "2026-07-16",
"issuer_name": "CRESCENT BIOPHARMA, INC.",
"issuer_trading_symbol": "CBIO",
"owner_name": "Kiselak Tomas",
"is_director": true,
"is_officer": false,
"is_ten_percent_owner": true,
"is_other": false,
"security_type": "non_derivative",
"record_type": "transaction",
"security_title": "Ordinary Shares",
"transaction_timeliness": "O",
"aff_10b5_one": false,
"transaction_date": "2026-07-16",
"transaction_code": "P",
"equity_swap_involved": false,
"transaction_shares": 853450,
"transaction_price_per_share": 14.5,
"transaction_acquired_disposed": "A",
"shares_owned_following_transaction": 3601316,
"transaction_value": 12375025,
"not_subject_to_section_16": false,
"direct_or_indirect": "I",
"nature_of_ownership": "By Fairmount Healthcare Fund II L.P.",
"footnotes": [
{
"id": "F1",
"description": "Fairmount Funds Management LLC (\"Fairmount\") is the investment manager for Fairmount Healthcare Fund II L.P. The managers of Fairmount are Peter Harwin and Tomas Kiselak. Fairmount, Mr. Harwin, and Mr. Kiselak disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein."
}
],
"remarks": "Fairmount may be deemed a director by deputization of Issuer by virtue of the fact that Peter Harwin serves on the board of directors of the Issuer and is a manager of Fairmount."
},
{
"tickers": [
"CBIO",
"GLYC"
],
"issuer_cik": "0001253689",
"owner_cik": "0001769651",
"accession_number": "0001104659-26-085113",
"form_type": "4",
"filing_date": "2026-07-20",
"period_of_report": "2026-07-16",
"issuer_name": "CRESCENT BIOPHARMA, INC.",
"issuer_trading_symbol": "CBIO",
"owner_name": "Fairmount Healthcare Fund II L.P.",
"is_director": true,
"is_officer": false,
"is_ten_percent_owner": true,
"is_other": false,
"security_type": "non_derivative",
"record_type": "transaction",
"security_title": "Ordinary Shares",
"transaction_timeliness": "O",
"aff_10b5_one": false,
"transaction_date": "2026-07-16",
"transaction_code": "P",
"equity_swap_involved": false,
"transaction_shares": 853450,
"transaction_price_per_share": 14.5,
"transaction_acquired_disposed": "A",
"shares_owned_following_transaction": 3601316,
"transaction_value": 12375025,
"not_subject_to_section_16": false,
"direct_or_indirect": "I",
"nature_of_ownership": "By Fairmount Healthcare Fund II L.P.",
"footnotes": [
{
"id": "F1",
"description": "Fairmount Funds Management LLC (\"Fairmount\") is the investment manager for Fairmount Healthcare Fund II L.P. The managers of Fairmount are Peter Harwin and Tomas Kiselak. Fairmount, Mr. Harwin, and Mr. Kiselak disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein."
}
],
"remarks": "Fairmount may be deemed a director by deputization of Issuer by virtue of the fact that Peter Harwin serves on the board of directors of the Issuer and is a manager of Fairmount."
}
]
}
// trimmed to 2 resultsThe response includes every Form 4 record; this page keeps open-market purchases and sales on common stock and removes duplicate joint-filer rows.
Other insider activity (not market trades) · 32 records
- Tax withholding (sold to cover)16 records
- Grants and awards16 records
Reported on Form 4 but not purchases or sales in the market, so not counted in the totals above.
How to read this page
- Open-market purchase or sale
- A buy or sell of the company's stock at market price. Grants, option exercises, shares withheld for tax, gifts and employee stock plan purchases are listed separately and not counted.
- Filing date
- Insiders have two business days to report a trade. Totals and the chart use the filing date, when the trade became public.
- Counted once
- When several owners (a fund and its partners, say) report the same trade, it's counted once. Corrected filings replace the originals.
Frequently asked questions
Has Crescent Biopharma, Inc.'s CEO sold stock?
No. Joshua T. Brumm (CEO) made no open-market sales filed as CEO in the last 12 months.
How current is CBIO’s insider data?
These are CBIO Form 4 filings from the last year, refreshed daily. The Massive Form 4 API has the full, continuously updated record.
What counts as an open-market buy or sell?
Only purchases and sales at the market price. Option exercises, grants, gifts, and shares withheld for taxes are reported on Form 4 but are left out of the buy and sell totals.
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Track CBIO insider trades with your agent
This page joins two Massive endpoints: Form 4 filings and daily prices. Ask an agent to watch for new filings:
Using the Massive API (massive.com/docs/llms.txt), check Form 4 filings for CBIO every day with transaction_code=P and tell me when an insider files an open-market purchase, with their role, shares, price and the filing link.
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