MBX Biosciences, Inc. Common Stock
MBX Biosciences, Inc. Common Stock (MBX) Stock Ownership
Institutional vs insider vs public ownership from 13F and float data — top holders, activity, and insider trades below.
SEC 13F · FMP · MBX · as of Sep 30, 2025
Ownership Breakdown
134
Institutional Holders
▲ 42 vs Q2
$836.36M
Total Inst. Value
▲ $416.03M vs Q2
33.59M
Shares Outstanding
freeFloat 43.49%
47.79M
13F Shares Held
▲ 10.95M vs Q2
Institutional ownership = 13F shares ÷ total outstanding. Insider % = 100 − free float. Public % = free float − institution %. Data: FMP /symbol-positions-summary + /shares-float + SEC EDGAR.
Top Institutional Holders
MBX largest shareholders · institutional ownership
Q3 2025 · SEC 13F
Showing top 10 holders
| Holder | Shares | % Owned | Weight | Value | Reported | Change |
|---|---|---|---|---|---|---|
FRAZIER LIFE SCIENCES MANAGEMENT, L.P. pharmaceutical preparations | 6.65M | 19.45% | 19.45% | $116.41B | Nov 14, 2025 | ▲ 666.7K |
WELLINGTON MANAGEMENT GROUP LLP pharmaceutical preparations | 4.82M | 14.10% | 14.10% | $84.41B | Nov 14, 2025 | ▲ 2.56M |
ORBIMED ADVISORS LLC pharmaceutical preparations | 4.00M | 11.70% | 11.70% | $70.05B | Nov 14, 2025 | — held |
NEA MANAGEMENT COMPANY, LLC pharmaceutical preparations | 3.61M | 10.57% | 10.57% | $63.25B | Nov 14, 2025 | — held |
DEEP TRACK CAPITAL, LP pharmaceutical preparations | 3.15M | 9.21% | 9.21% | $55.13B | Nov 14, 2025 | ▲ 961.4K |
NVP ASSOCIATES, LLC pharmaceutical preparations | 2.14M | 6.25% | 6.25% | $37.39B | Nov 14, 2025 | — held |
ECOR1 CAPITAL, LLC pharmaceutical preparations | 2.12M | 6.21% | 6.21% | $37.16B | Nov 14, 2025 | ▲ 973.8K |
KYNAM CAPITAL MANAGEMENT, LP pharmaceutical preparations | 2.00M | 5.85% | 5.85% | $35.00B | Nov 14, 2025 | NEW |
BLACKROCK, INC. pharmaceutical preparations | 1.96M | 5.72% | 5.72% | $34.26B | Nov 12, 2025 | ▲ 945.9K |
VANGUARD GROUP INC pharmaceutical preparations | 1.68M | 4.90% | 4.90% | $29.35B | Nov 7, 2025 | ▲ 633.7K |
Data from SEC Form 13F filings. Ownership bar normalised to largest holder. Change flags: isNew / isSoldOut / changeInSharesNumber (FMP extract-analytics/holder).
Institutional Activity
Q3 2025 vs prior quarter
Q3 2025
20
Increased
+9.88M shares19
New Positions
first time holders7
Decreased
−1.38M shares0
Sold Out
fully exitedNet shares change (top 50)
+8.50M
+9.88M / −1.38M
Net new holders
+32
19 new / 0 exited
Based on top 50 institutional holders by position size. Fields: isNew, isSoldOut, changeInSharesNumber (FMP extract-analytics/holder, limit=50).
Insider Buying vs Selling
MBX insider trading · insider activity
Source: SEC Form 4
Insiders have been primarily selling shares recently. Selling may be driven by pre-scheduled Rule 10b5-1 plans rather than negative sentiment.
13
Buy transactions
4
Sell transactions
3.25
Buy/Sell ratio
$0M
Total disposed
Recent Insider Transactions
Showing 10 most recent · Common Stock only
| Name · Role | Date | Type | Shares | Price | Value | After Trans. | Filing |
|---|---|---|---|---|---|---|---|
Mathers Edward T director | Jun 4, 2026 | Award | 12,500 | $30.91 | $386.4K | 12.5K | Form 4 ↗ |
Pescovitz Ora H. director | Jun 4, 2026 | Award | 12,500 | $30.91 | $386.4K | 12.5K | Form 4 ↗ |
Heron Patrick J
| Jun 4, 2026 | Award | 12,500 | $30.91 | $386.4K | 12.5K | Form 4 ↗ |
Stelzer Laurie director | Jun 4, 2026 | Award | 12,500 | $30.91 | $386.4K | 12.5K | Form 4 ↗ |
Hoerter Steven L. director | Jun 4, 2026 | Award | 12,500 | $30.91 | $386.4K | 12.5K | Form 4 ↗ |
Ryder Steven director | Jun 4, 2026 | Award | 12,500 | $30.91 | $386.4K | 12.5K | Form 4 ↗ |
Aynechi Tiba director | Jun 4, 2026 | Award | 12,500 | $30.91 | $386.4K | 12.5K | Form 4 ↗ |
Azoulay Salomon Chief Medical Officer | May 8, 2026 | Sale | 15,003 | $38.30 | $574.6K | 14.8K | Form 4 ↗ |
Azoulay Salomon Chief Medical Officer | May 8, 2026 | Sale | 55,000 | $38.38 | $2.11M | 14.8K | Form 4 ↗ |
Azoulay Salomon Chief Medical Officer | May 6, 2026 | Sale | 231 | $29.54 | $6.8K | 14.8K | Form 4 ↗ |
Source: /insider-trading/search (FMP stable). Buy/Sell direction: acquisitionOrDisposition A=Buy, D=Sell. RSU vesting (M-Exempt) excluded from sentiment bar. All data from SEC EDGAR public filings.
About institutional & insider ownership
MBX Biosciences, Inc. Common Stock (MBX) is primarily owned by institutional investors, who hold approximately 100.0% of total shares outstanding. Company insiders own approximately 56.51%, while retail and public investors account for the remaining 0.00%.
The largest institutional shareholder of MBX Biosciences, Inc. Common Stock is FRAZIER LIFE SCIENCES MANAGEMENT, L.P., holding approximately 6.65 million shares — equal to 19.45% of outstanding shares — as of September 30, 2025.
A total of 134 institutional investors currently hold MBX stock, with a combined institutional value of approximately $836,364,529 as of the most recent 13F filing period.
Frequently asked questions
MBX ownershipMBX Biosciences, Inc. Common Stock (MBX) is primarily owned by institutional investors, who hold approximately 100.0% of shares. The largest shareholder is FRAZIER LIFE SCIENCES MANAGEMENT, L.P. with a 19.45% stake. Company insiders hold 56.51%. Data sourced from SEC Form 13F as of September 30, 2025.