Decagon AI Inc., a customer support startup, has raised $250 million in a new round of funding that triples its valuation to $4.5 billion, the latest sign of feverish investor demand for artificial intelligence services. The financing, which is set to be announced Wednesday, was led by Coatue Management and Index Ventures, with participation from Chemistry VC, Definition Capital and Starwood Capital Group. Existing investors including Andreessen Horowitz, Accel and Bain Capital Ventures also joi...