Sierra Raises $950M Series E at $15.8B Valuation — Bret Taylor's CX Agent Platform Now Handles Billions of Interactions for 40% of Fortune 50

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Sierra, co-founded by former Salesforce CEO Bret Taylor and ex-Google exec Clay Bavor, closed a $950M Series E led by Tiger Global and Google Ventures at $15.8B valuation. The company surpassed $150M ARR in eight quarters and now serves 40%+ of the Fortune 50, with agents handling mortgage origination, insurance claims, subscription management, and healthcare revenue cycle — far beyond basic support. In April, Sierra launched Ghostwriter, an 'agent as a service' that builds other agents from natural language descriptions.