QuantumSi is trading 5.5% lower at $1.21 on October 8, 2026, with biotech-sector weakness possibly contributing. - XBI is down 2.04% in the session; major U.S. indices are also lower, but by less than 0.5%. - No clear company-specific announcement explaining the decline surfaced in the search. The latest identified product update was the September 28 Proteus data announcement, which predates this move.