Rillet co-founder and CEO Gunther Kopp seems justifiably confident as we talk over Zoom a day after his company announced a $100 million raise at a $1 billion valuation. The startup has a shortage of accountants right now, which is driving growth of its AI-native accounting platform so much, it raised that cash in 48 hours without even trying. Rillet emerged from stealth two years ago. Since then, it has raised $200 million from top investors like ICONIQ, Drew Gannon, and Sequoia. It's also amassed 600 customers, most of whom are looking to ditch legacy accounting systems like Oracle and Net Suite, Kopp says.

A few weeks ago, Rillet held a board meeting and shared with investors its growth since its $70 million Series B last summer. Annualized revenue rate had doubled in the last quarter alone; the startup added new clients, many of them public companies, and an alliance with EY to introduce AI tools to the auditing giant. Its customers aren't piloting Rillet either, it said — they're yanking out ERP and accounting software from competitors like Intuit, Net Suite, or Oracle.

After that board meeting, text messages were fired, calls were made, and 48 hours later, Rillet was a unicorn. The company wasn't even looking to raise, Kopp said. Drew Gannon, the general partner at Iconiq who led the round, said that the deal came together fast but "it wasn't a cold start," he described. "Rillet had already proven it could win against the incumbents that have owned this category for decades," Gannon told Tech Crunch.

Rillet is one of many AI-native startups now giving legacy players a run for relevance. Earlier this year, software stocks on the public market dipped as investors worried about how emerging AI tools would affect them. Kopp thinks there's some truth to that. "AI is going to come hard at these legacy players," he said because it is giving customers compelling alternatives. Rillet, for example, was built for AI agents, not humans, letting humans work alongside the AI agents on corporate bookkeeping. Rillet clients range from laundromats to the NFL Hall of Fame. Some 50% of Rillet customers come from Intuit, 30% from Net Suite and Oracle, and 20% from SAP, Workday, and Microsoft products, he said.