Sierra, an AI startup co-founded by Bret Taylor, Chairman of the OpenAI Board, and former Google executive Clay Bavor, has raised $950 million in a Series E funding round. This latest investment brings Sierra's valuation to $15.8 billion. The funding round was led by Tiger Global and GV, with participation from Benchmark, Sequoia, and Greenoaks.Sierra specializes in AI customer service agents aimed at automating support for enterprise clients. The company reports that its annualized recurring revenue has exceeded $150 million over the past eight quarters. Sierra employs a "model swarm" approach with a proprietary fine-tuning layer to enhance its AI services. Previously, Sierra raised $175 million in October 2024 at a $4.5 billion valuation.