Welcome to ZoomInfo's financial results conference call for the fourth quarter and full year 2025. We entered the year strong with record quarterly revenue and results that beat the top end of our guidance. In the fourth quarter, we delivered revenue of $319 million, up 3% year-over-year, and adjusted operating income of $123 million, representing a margin of 38%, once again returning to Rule of 40 performance. In 2025, we delivered $1.25 billion in revenue with an AOI margin of 36%, and we grew free cash flow per share by more than 10% for the year.
We also returned more than $400 million in capital to shareholders through share repurchases, all while investing in the business to drive innovation and build the GTM intelligence platform of the future. Upmarket again grew 6% in our seasonally largest upmarket quarter, triple the upmarket growth rate from a year ago. Success in our operations business continues to be driven by demand for actionable, high-quality data, a key foundation to power AI use cases, and operations again grew more than 20% year-over-year in the quarter. AI development tools have lowered the cost of building software, but they don't erode our advantage at the data layer.
We are more than a horizontal software company, and AI has been an accelerant, expanding the use cases we power and the workflows where ZoomInfo shows up. Revenue teams still operate across six or more separate tools: CRM, contact databases, conversation intelligence, research platforms, AI assistants, and spreadsheets. Given the unprecedented negative sentiment of public markets toward anything software-related, we believe our share price is completely disconnected from economic reality. We have already retired nearly 25% of our shares since the start of 2023, and we intend to opportunistically deploy this additional $1 billion while continuing to double down on execution.