FINANCIAL INSTITUTIONS INC

FROM OUR INDEPENDENT BOARD CHAIRFELLOW SHAREHOLDERS:

On behalf of the Board of Directors of Financial Institutions, Inc., I would like to sincerely thank you for your interest and investment in our Company. Whether you are a long-time shareholder, or joined us through our December 2024 common equity offering, we are proud to have you alongside us. Our Board and executive management team are focused on strong execution of community banking fundamentals and enhancing our profitability in a manner that prioritizes safety and soundness, in order to deliver long-term value to you, our shareholders. Our operating model and strategic framework are designed around this value creation goal as well as our vision of being a high-performing community bank offering a simple, connected and trusted experience in the markets we serve.2024 was a year in which our Company persevered through tremendous challenges, executed at a high level on strategic initiatives that position us well for the future, and focused on delivering meaningful customer

experiences across our commercial, retail and wealth management lines of business in support of organic and sustainable growth. Our fourth quarter public equity offering and subsequent balance sheet restructuring were bold actions that provided strong momentum into 2025 and position us well to deliver improved earnings and profitability, both this year and in future periods. We understand the importance of an engaged and evolving Board in stewarding our Company’s success. Consistent with our commitment to board refreshment, we appointed Angela Panzarella to our Board in January 2025 and have also nominated Robert Schrader to serve as a Director. Ms. Panzarella spent the majority of her career in the highly regulated health care industry, overseeing corporate strategy, financial and business operations, business development and more. Mr. Schrader brings more than 25 years of experience in corporate finance and public accounting, and we believe his expertise and counsel will be very valuable as we continue to execute on our strategic objectives. We are pleased to recommend these two highly qualified and capable individuals to serve as independent directors. As we welcome them, I would like recognize the contributions of Samuel Gullo, who will be retiring as a director at the 2025 Annual Meeting of Shareholders. The Company has benefited from Mr. Gullo’s dedicated service for 25 years. His unwavering commitment and impactful contributions to the Board of Directors have been instrumental in shaping our Company’s future. His passion for the organization has inspired us all and he will certainly be missed.

We greatly value engagement with our shareholders and seek opportunities to proactively engage regularly, through conference attendance, virtual and in-person meetings, and publicly available quarterly investor calls. Your engagement in our annual meeting is also important, and we encourage you to read this 2025 Proxy Statement and vote online to ensure that you are represented. Thank you again for your support of our Company. Cordially, Susan R. HollidayChair of the BoardApril 14, 2025

Financial Institutions, Inc.

FROM OUR CEOFELLOW SHAREHOLDERS:

Our Company successfully navigated an incredibly dynamic 2024, rising above challenges, to execute strategic initiatives that support our strong focus on organically growing our community banking franchise and position us for improved performance not only in 2025, but for the years to come. From the sale of the assets of our insurance subsidiary in the second quarter, to our decision to wind down our Banking-as-a-Service offering as announced in the third quarter, we have taken strategic actions in the last year that allow us to focus on organically growing our core community banking franchise. More recently, in the fourth quarter of 2024, we completed a successful and oversubscribed common equity public offering and balance sheet restructuring that is expected to contribute meaningfully to improved financial results and profitability metrics moving forward. We accomplished these successful outcomes while also responding to the deposit-related fraud event experienced in the first quarter of 2024 and, more recently, reaching a settlement related to a longstanding auto lending litigation.

As always, we remained a committed and engaged partner to the communities we serve, supporting them through grants, financial literacy education, volunteerism and more. Our 2024 Community Report details many of the ways we have given and continue to give back to our communities.

We cordially invite you to our 2025 Annual Meeting of Shareholders on Wednesday, May 28, 2025, at 10:00 am, Eastern Time. The meeting will be held in virtual format through a live webcast, accessible at www.virtualshareholdermeeting.com/FISI2025.

You will be asked to vote on several items including the election of directors, compensation of our named executive officers (the say-on-pay vote), an amendment to our long-term incentive plan, and the ratification of the appointment of RSM US LLP to serve as our independent registered public accounting firm for 2025. Your vote is important, and we encourage you to read the proxy statement and vote your shares as promptly as possible. Proxy materials are again being provided via the internet this year, expediting delivery to shareholders, supporting effective expense management and reducing the environmental impact of our meeting.

Information on how to attend the annual meeting, vote and submit questions is provided in the attached notice of annual meeting.

On behalf of the Company’s executive and senior leadership team, I thank you for your continued support of and investment in Financial Institutions, Inc.Sincerely, Martin K. BirminghamPresident and Chief Executive OfficerApril 14, 2025

Financial Institutions, Inc.