We executed well across our strategic priorities, delivered another quarter of strong financial results, accelerated upmarket growth, and raised our guidance for the year, which now calls for positive revenue growth in 2025. All these inputs should drive accelerating free cash flow per share growth over the next few years and beyond. In Q2, GAAP revenue was $307 million, and adjusted operating income was $105 million, a margin of 34%, both above the high end of guidance. We now have 1,884 customers with more than $100,000 in ACV, a sequential increase of 16 customers and a year-over-year increase of 87 customers.
ACV growth in the quarter from that cohort was materially higher than last Q2 as our largest customers continue to expand and embed more of our data and agents in their workflows. We added customers to our million dollar cohort, driving sequential and year over year growth in total ACV as well as the average ACV per million dollar customer. Upmarket ACV accelerated from 3% year-over-year growth in Q1 to 4% year-over-year growth in Q2. Net revenue retention improved to 89% in the quarter, up 4 percentage points in three quarters, with upmarket retention the highest it has been in several years.
Today, 72% of our ACV is coming from larger upmarket customers, an area where we see higher levels of profitability and accelerating revenue growth as we successfully execute on our transition upmarket. During our last earnings call, we made clear our intention to build the Go-To-Market Intelligence platform. Second, Go-To-Market Studio is our operational counterpart to Copilot, enabling sales leaders and revenue operations teams to architect campaigns and strategies. We deployed some of that excess headcount into upmarket sales roles where we continue to add headcount.