4 institutions reported holding $2.5M of OCTAVE SPECIALTY GROUP INC (AMBC.WS) in SEC 13F filings for 2026-03-31. Largest institutional holders: GROUP ONE TRADING LLC ($1.9M), IMC-Chicago, LLC ($560,790), SIMPLEX TRADING, LLC ($101,370), HRT FINANCIAL LP ($0). Source: SEC Form 13F.
| Rank | Institution | Value | Shares | Change |
|---|---|---|---|---|
| 1 | GROUP ONE TRADING LLC | $1.9M | 399,500 | Trimmed |
| 2 | IMC-Chicago, LLC | $560,790 | 120,600 | Trimmed |
| 3 | SIMPLEX TRADING, LLC | $101,370 | 21,800 | Trimmed |
| 4 | HRT FINANCIAL LP | $0 | 0 | Exited |
Source: SEC Form 13F filings · as of 2026-03-31