Spero Therapeutics, Inc. (SPRO) Ownership
SPRO ownership summary
as of October 18, 2026- Institutions
- 18.4% of shares outstanding
- Insiders
- 22.66% of shares outstanding
- Shares outstanding
- 58.2M
- Float
- 47.1M shares available to trade
- Short interest
- 1.64% 795K shares short
- Days to cover
- 1.06 short interest down 18.6% vs prior month
- Institutions 18.37%
- Insiders 22.66%
- Other investors 58.97%
SPRO top institutional holders
20 largest| # | Holder | % of shares | Shares | Value | Change | Reported |
|---|---|---|---|---|---|---|
| 1 | GSK PLC | 15.78% | 9.2M | $10.1M | — | June 30, 2026 |
| 2 | Pfizer Inc | 4.06% | 2.4M | $2.6M | — | June 30, 2026 |
| 3 | Vanguard Capital Management, LLC | 3.50% | 2.0M | $2.2M | +236,346 (+13.1%) | June 30, 2026 |
| 4 | Renaissance Technologies Corp | 1.63% | 948K | $1.0M | −241,331 (−20.3%) | June 30, 2026 |
| 5 | Alphabet Inc | 1.53% | 890K | $978,977 | — | June 30, 2026 |
| 6 | Susquehanna International Group, LLP | 1.30% | 759K | $835,219 | +426,175 (+127.9%) | June 30, 2026 |
| 7 | BlackRock Inc | 1.02% | 594K | $653,844 | +161,202 (+37.2%) | June 30, 2026 |
| 8 | Geode Capital Management, LLC | 0.97% | 566K | $622,962 | +46,407 (+8.9%) | June 30, 2026 |
| 9 | Two Sigma Investments LLC | 0.66% | 383K | $421,095 | −502,817 (−56.8%) | June 30, 2026 |
| 10 | Arrowstreet Capital Limited Partnership | 0.57% | 333K | $366,267 | +332,970 (0.0%) | June 30, 2026 |
| 11 | Vanguard Fiduciary Trust Co | 0.49% | 288K | $316,413 | +23,533 (+8.9%) | June 30, 2026 |
| 12 | GSA Capital Partners LLP | 0.49% | 286K | $314,497 | +7,602 (+2.7%) | June 30, 2026 |
| 13 | Dimensional Fund Advisors, Inc. | 0.47% | 275K | $302,302 | +245,052 (+823.2%) | June 30, 2026 |
| 14 | The Goldman Sachs Group Inc | 0.44% | 257K | $282,684 | +256,985 (0.0%) | June 30, 2026 |
| 15 | State Street Corp | 0.37% | 215K | $236,226 | — | June 30, 2026 |
| 16 | Jane Street Group LLC | 0.27% | 158K | $173,907 | +51,752 (+48.7%) | June 30, 2026 |
| 17 | UBS Group AG | 0.24% | 140K | $153,648 | +136,671 (+4,542.1%) | June 30, 2026 |
| 18 | Bridgeway Capital Management, LLC | 0.20% | 115K | $126,280 | — | June 30, 2026 |
| 19 | Northern Trust Corp | 0.19% | 108K | $119,101 | −12,710 (−10.5%) | June 30, 2026 |
| 20 | Point72 Asset Management, L.P. | 0.18% | 104K | $114,815 | +44,709 (+74.9%) | June 30, 2026 |
Value at the latest close. Change = shares bought or sold in the latest quarterly filing (13F). In the top 20, 12 holders added 2.0M shares and 3 cut 757K.
SPRO top mutual fund and ETF holders
18 largest| # | Holder | % of shares | Shares | Value | Change | Reported |
|---|---|---|---|---|---|---|
| 1 | Vanguard MStar Total Stk Mkt Idx Invest | 2.40% | 1.4M | $1.5M | — | August 31, 2026 |
| 2 | Mackenzie GQE US Small Cap F8 | 0.85% | 497K | $546,840 | +497,127 (0.0%) | July 31, 2026 |
| 3 | iShares Micro-Cap ETF | 0.25% | 144K | $158,662 | −995 (−0.7%) | September 30, 2026 |
| 4 | Fidelity Total Market Index | 0.18% | 108K | $118,483 | — | August 31, 2026 |
| 5 | Invesco NASDAQ Future Gen 200 ETF | 0.17% | 98K | $108,180 | — | September 30, 2026 |
| 6 | Fidelity Extended Market Index | 0.12% | 72K | $78,896 | −177,218 (−71.2%) | August 31, 2026 |
| 7 | Fidelity Series Total Market Index | 0.12% | 70K | $76,771 | — | August 31, 2026 |
| 8 | EA Bridgeway Ultra-Small Company Mkt ETF | 0.11% | 64K | $70,338 | — | September 30, 2026 |
| 9 | Acuitas US Microcap Institutional | 0.10% | 56K | $62,103 | +56,457 (0.0%) | June 30, 2026 |
| 10 | Bridgeway Omni Small-Cap Value N | 0.09% | 50K | $55,000 | — | June 30, 2026 |
| 11 | Dimensional Global Trgtd Value USD Acc | 0.06% | 32K | $35,408 | — | August 31, 2026 |
| 12 | Schwab Total Stock Market Index | 0.05% | 29K | $31,422 | — | August 31, 2026 |
| 13 | Invesco RAFI US 1500 Small-Mid ETF | 0.05% | 27K | $29,763 | — | September 30, 2026 |
| 14 | Vanguard U.S. Eq Idx £ Acc | 0.04% | 25K | $27,991 | — | August 31, 2026 |
| 15 | Vanguard Balanced Index Inv | 0.04% | 24K | $26,594 | — | August 31, 2026 |
| 16 | Vanguard MStar Inst Ttl StkMktIdxInstlPl | 0.04% | 23K | $25,102 | — | August 31, 2026 |
| 17 | Dimensional VA US Targeted Value | 0.03% | 15K | $16,641 | — | August 31, 2026 |
| 18 | 1290 VT Micro Cap K | 0.02% | 10K | $11,187 | — | August 31, 2026 |
Funds report holdings monthly or quarterly; dates differ by fund.
SPRO insider transactions
latest 4| Date | Name | Transaction | Price | Shares | Value |
|---|---|---|---|---|---|
| 2026-02-06 | Esther Rajavelu | Sell | $2.36 | 87,917 | $207,484 |
| 2026-02-02 | Esther Rajavelu | Sell | $2.20 | 18,442 | $40,572 |
| 2025-11-07 | Esther Rajavelu | Sell | $2.37 | 40,270 | $95,440 |
| 2025-08-28 | Ankit Mahadevia | Sell | $1.97 | 6,572 | $12,947 |
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.
SPRO shares outstanding
Year-end shares outstanding, adjusted for splits.
Who owns SPRO
Institutional investors own 18.4% of Spero Therapeutics's shares and insiders 22.66%. The largest holder is GSK PLC with 15.78% of the shares (9.2M), as of June 30, 2026. Among the top 20 institutions, 12 added shares and 3 reduced their stake in the latest filings. Short interest is 1.64% of the float, or 1.06 days of average trading volume. The share count rose 798.9% since 2016.
Related: SPRO analyst forecast, SPRO key metrics. See the SPRO stock overview for the latest quote and news.
SPRO ownership FAQ
Who owns the most Spero Therapeutics stock?
The largest shareholders of Spero Therapeutics are GSK PLC (15.78%), Pfizer Inc (4.06%), Vanguard Capital Management, LLC (3.50%), Renaissance Technologies Corp (1.63%), Alphabet Inc (1.53%).
What percentage of Spero Therapeutics is owned by institutions?
Institutions hold 18.4% of Spero Therapeutics's shares outstanding; insiders hold 22.66%.
Which funds own Spero Therapeutics?
The largest fund holders of Spero Therapeutics are Vanguard MStar Total Stk Mkt Idx Invest (2.40%), Mackenzie GQE US Small Cap F8 (0.85%), iShares Micro-Cap ETF (0.25%), Fidelity Total Market Index (0.18%), Invesco NASDAQ Future Gen 200 ETF (0.17%).
What is Spero Therapeutics's short interest?
795K shares of Spero Therapeutics were sold short, 1.64% of the float; at the average daily volume it would take 1.06 days to cover.
Are insiders buying or selling Spero Therapeutics?
Of the latest 4 reported insider transactions in Spero Therapeutics (since August 28, 2025), 0 were purchases and 4 were sales.
How many shares of Spero Therapeutics are outstanding?
Spero Therapeutics has 58.2M shares outstanding, of which 47.1M are in the public float.