Rillet, a two-year-old startup building what it calls the first truly AI-native accounting platform, has raised a $100 million Series C at a $1 billion valuation, the company told Fortune exclusively—joining the ranks of AI-era unicorns racing to unseat decades-old enterprise software giants. The round, led by ICONIQ with participation from returning backers Sequoia Capital, Andreessen Horowitz and Oak HC/FT, plus new investors including Bain Capital Ventures, Sequoia Global Equities, Battery Ve...