Exhibit 99.1 Financial Institutions, Inc. Reports Third Quarter 2025 Results, Including Net Income Available to Common Shareholders of $20.1 million, or$0.99 per Diluted Share Quarterly results highlighted by double-digit net interest margin expansion, record net interest income, and strong noninterest income, in addition to loan and deposit growth WARSAW, N.Y., October 23, 2025 – Financial Institutions, Inc. (NASDAQ: FISI) (the "Company," "we" or "us"), parent company of Five Star Bank (the "Bank") and Co ...