Sionna Therapeutics, Inc. (SION) Ownership
SION ownership summary
as of October 18, 2026- Institutions
- 101.6% of shares outstanding
- Insiders
- 7.88% of shares outstanding
- Shares outstanding
- 45.2M
- Float
- 20.5M shares available to trade
- Short interest
- 13.63% 3.8M shares short
- Days to cover
- 2.55 short interest down 4.2% vs prior month
- Institutions 101.60%
- Insiders 7.88%
SION top institutional holders
20 largest| # | Holder | % of shares | Shares | Value | Change | Reported |
|---|---|---|---|---|---|---|
| 1 | RA Capital Management, LLC | 21.91% | 9.9M | $38.5M | — | June 30, 2026 |
| 2 | TPG GP A, LLC | 14.37% | 6.5M | $25.3M | — | June 30, 2026 |
| 3 | Viking Global Investors LP | 7.07% | 3.2M | $12.4M | — | June 30, 2026 |
| 4 | Atlas Venture Life Science Advisors, LLC | 6.63% | 3.0M | $11.7M | — | June 30, 2026 |
| 5 | Orbimed Advisors LLC | 5.65% | 2.6M | $9.9M | −974,825 (−27.6%) | June 30, 2026 |
| 6 | Enavate Sciences GP, LLC | 5.48% | 2.5M | $9.6M | — | June 30, 2026 |
| 7 | Adage Capital Partners Gp LLC | 3.54% | 1.6M | $6.2M | +1.4M (+966.7%) | June 30, 2026 |
| 8 | JPMorgan Chase & Co | 3.30% | 1.5M | $5.8M | +25,494 (+1.7%) | June 30, 2026 |
| 9 | BlackRock Inc | 3.26% | 1.5M | $5.7M | +178,902 (+13.8%) | June 30, 2026 |
| 10 | Jennison Associates LLC | 2.59% | 1.2M | $4.6M | −279,087 (−19.2%) | June 30, 2026 |
| 11 | Citadel Advisors Llc | 2.54% | 1.1M | $4.5M | −19,295 (−1.7%) | June 30, 2026 |
| 12 | Vanguard Capital Management, LLC | 2.50% | 1.1M | $4.4M | +102,504 (+10.0%) | June 30, 2026 |
| 13 | State Street Corp | 2.26% | 1.0M | $4.0M | +265,307 (+35.1%) | June 30, 2026 |
| 14 | Perceptive Advisors LLC | 2.00% | 905K | $3.5M | +246,561 (+37.4%) | June 30, 2026 |
| 15 | Deerfield Management Co | 1.51% | 681K | $2.6M | −289,674 (−29.8%) | June 30, 2026 |
| 16 | Siren, L.L.C. | 1.35% | 611K | $2.4M | +310,515 (+103.5%) | June 30, 2026 |
| 17 | T. Rowe Price Associates, Inc. | 1.06% | 478K | $1.9M | −278,360 (−36.8%) | June 30, 2026 |
| 18 | Eventide Asset Management, LLC | 1.05% | 475K | $1.8M | −170,549 (−26.4%) | June 30, 2026 |
| 19 | Geode Capital Management, LLC | 1.01% | 457K | $1.8M | +67,273 (+17.3%) | June 30, 2026 |
| 20 | Casdin Capital, LLC | 0.88% | 400K | $1.6M | +400,000 (0.0%) | June 30, 2026 |
Value at the latest close. Change = shares bought or sold in the latest quarterly filing (13F). In the top 20, 9 holders added 3.0M shares and 6 cut 2.0M.
SION top mutual fund and ETF holders
20 largest| # | Holder | % of shares | Shares | Value | Change | Reported |
|---|---|---|---|---|---|---|
| 1 | Vanguard MStar Total Stk Mkt Idx Invest | 2.07% | 935K | $3.6M | — | August 31, 2026 |
| 2 | PGIM Jennison Health Sciences Z | 2.06% | 934K | $3.6M | +444,027 (+90.7%) | August 31, 2026 |
| 3 | iShares Russell 2000 ETF | 1.08% | 486K | $1.9M | −5,632 (−1.1%) | September 30, 2026 |
| 4 | Eventide Healthcare & Life Sciences I | 1.05% | 475K | $1.8M | −169,555 (−26.3%) | June 30, 2026 |
| 5 | Candriam Eqs L Biotech C USD Cap | 0.52% | 237K | $921,203 | +236,813 (0.0%) | March 31, 2026 |
| 6 | iShares Biotechnology ETF | 0.46% | 207K | $806,284 | −1,568 (−0.8%) | September 30, 2026 |
| 7 | Fidelity Small Cap Index | 0.45% | 202K | $785,150 | +1,622 (+0.8%) | July 31, 2026 |
| 8 | iShares Russell 2000 Growth ETF | 0.39% | 175K | $679,641 | −221 (−0.1%) | September 30, 2026 |
| 9 | Artisan International Small-Mid Investor | 0.26% | 116K | $452,959 | +116,442 (0.0%) | June 30, 2026 |
| 10 | Vanguard Russell 2000 ETF | 0.23% | 106K | $411,558 | +2,361 (+2.3%) | August 31, 2026 |
| 11 | Schwab US Small-Cap ETF™ | 0.22% | 101K | $394,197 | +63 (+0.1%) | September 30, 2026 |
| 12 | UTM IM GBP AXA Framlington Biotech | 0.16% | 73K | $282,095 | +72,518 (0.0%) | July 31, 2026 |
| 13 | ALPS Medical Breakthroughs ETF | 0.13% | 59K | $231,358 | — | September 30, 2026 |
| 14 | Vanguard US Momentum Factor ETF | 0.12% | 55K | $214,176 | +9,080 (+19.7%) | June 30, 2026 |
| 15 | Driehaus Micro Cap Growth | 0.10% | 47K | $182,616 | — | July 31, 2026 |
| 16 | Schwab Small Cap Index | 0.10% | 45K | $173,782 | — | August 31, 2026 |
| 17 | Vanguard Health Care ETF | 0.09% | 41K | $159,965 | +180 (+0.4%) | August 31, 2026 |
| 18 | Stt Strt SPDR® Russell2000 US SmCapETF | 0.08% | 38K | $147,307 | +1,824 (+5.1%) | August 31, 2026 |
| 19 | iShares Nasdaq US Biotech ETF USD Acc | 0.08% | 37K | $142,732 | +316 (+0.9%) | September 30, 2026 |
| 20 | iShares Russell 2000 Small-Cap Idx Instl | 0.08% | 34K | $134,084 | — | August 31, 2026 |
Funds report holdings monthly or quarterly; dates differ by fund.
SION insider transactions
latest 20| Date | Name | Transaction | Price | Shares | Value |
|---|---|---|---|---|---|
| 2026-04-18 | Peter A Thompson | Sell | $44.52 | 2,948 | $131,245 |
| 2026-04-18 | Orbimed Advisors Llc | Sell | $44.52 | 2,948 | $131,245 |
| 2026-04-17 | Orbimed Advisors Llc | Sell | $44.68 | 52,397 | $2.3M |
| 2026-04-17 | Peter A Thompson | Sell | $44.68 | 52,397 | $2.3M |
| 2026-04-16 | Orbimed Advisors Llc | Sell | $45.34 | 226,906 | $10.3M |
| 2026-04-16 | Peter A Thompson | Sell | $45.34 | 226,906 | $10.3M |
| 2026-04-15 | Orbimed Advisors Llc | Sell | $44.64 | 235,863 | $10.5M |
| 2026-04-15 | Peter A Thompson | Sell | $44.64 | 235,863 | $10.5M |
| 2026-04-14 | Orbimed Advisors Llc | Sell | $44.51 | 47,814 | $2.1M |
| 2026-04-14 | Peter A Thompson | Sell | $44.51 | 47,814 | $2.1M |
| 2026-02-03 | Orbimed Advisors Llc | Sell | $44.58 | 29,063 | $1.3M |
| 2026-02-03 | Peter A Thompson | Sell | $44.58 | 29,063 | $1.3M |
| 2026-02-02 | Orbimed Advisors Llc | Sell | $44.57 | 1,890 | $84,237 |
| 2026-02-02 | Peter A Thompson | Sell | $44.57 | 1,890 | $84,237 |
| 2026-01-22 | Tpg Gp A, Llc | Sell | $40.00 | 250,000 | $10.0M |
| 2025-12-24 | Orbimed Advisors Llc | Sell | $44.55 | 33,356 | $1.5M |
| 2025-12-24 | Peter A Thompson | Sell | $44.55 | 33,356 | $1.5M |
| 2025-12-19 | Orbimed Advisors Llc | Sell | $44.49 | 875 | $38,929 |
| 2025-12-19 | Peter A Thompson | Sell | $44.49 | 875 | $38,929 |
| 2025-12-18 | Orbimed Advisors Llc | Sell | $44.49 | 100 | $4,449 |
Reported trades by company officers, directors and other filers (including disclosures by members of Congress where EODHD lists them). "—" where the filing gives no share count.
SION shares outstanding
Year-end shares outstanding, adjusted for splits.
Who owns SION
Institutional investors own 101.6% of Sionna Therapeutics's shares and insiders 7.88%. The largest holder is RA Capital Management, LLC with 21.91% of the shares (9.9M), as of June 30, 2026. Among the top 20 institutions, 9 added shares and 6 reduced their stake in the latest filings. Short interest is 13.63% of the float, or 2.55 days of average trading volume. The share count fell 9.4% since 2023.
Related: SION analyst forecast, SION key metrics. See the SION stock overview for the latest quote and news.
SION ownership FAQ
Who owns the most Sionna Therapeutics stock?
The largest shareholders of Sionna Therapeutics are RA Capital Management, LLC (21.91%), TPG GP A, LLC (14.37%), Viking Global Investors LP (7.07%), Atlas Venture Life Science Advisors, LLC (6.63%), Orbimed Advisors LLC (5.65%).
What percentage of Sionna Therapeutics is owned by institutions?
Institutions hold 101.6% of Sionna Therapeutics's shares outstanding; insiders hold 7.88%.
Which funds own Sionna Therapeutics?
The largest fund holders of Sionna Therapeutics are Vanguard MStar Total Stk Mkt Idx Invest (2.07%), PGIM Jennison Health Sciences Z (2.06%), iShares Russell 2000 ETF (1.08%), Eventide Healthcare & Life Sciences I (1.05%), Candriam Eqs L Biotech C USD Cap (0.52%).
What is Sionna Therapeutics's short interest?
3.8M shares of Sionna Therapeutics were sold short, 13.63% of the float; at the average daily volume it would take 2.55 days to cover.
Are insiders buying or selling Sionna Therapeutics?
Of the latest 20 reported insider transactions in Sionna Therapeutics (since December 18, 2025), 0 were purchases and 20 were sales.
How many shares of Sionna Therapeutics are outstanding?
Sionna Therapeutics has 45.2M shares outstanding, of which 20.5M are in the public float.