The institutional bet on enterprise AI was that the incumbents would absorb it. Salesforce had the customer data. ServiceNow had the workflow. Both spent 2024 and 2025 announcing agent products built on top of decades of seat licenses, telling Wall Street the moat held because the data could not be replatformed and the customer would not move. The thesis required one premise. That an upstart could not reach the Fortune 50 fast enough to matter before the incumbents shipped their version. On May 4, 2026, Sierra closed a $950 million Series E at a $15.8 billion post-money valuation. Tiger Global led. GV co-led. Benchmark, Sequoia, and Greenoaks rolled. The valuation was $10 billion six months earlier. ARR was $100 million in November. By early February it was $150 million. Read the customer line. Sierra has more than 40 percent of the Fortune 50 already paying for AI customer service agents. The Fortune 50 is the durable Salesforce base. The buyer who is supposed to take the call from the incumbent rep about Agentforce. The buyer whose IT team has spent ten years standardizing on the per-seat license. That buyer signed Sierra. The CEO is the detail. Bret Taylor was Salesforce's Co-CEO with Marc Benioff from 2021 to 2023. He sat next to the man who is now telling Wall Street that per-user pricing is the new AI norm. Taylor left, took Clay Bavor from Google, and built the company that proves Benioff is wrong on the use case Salesforce was supposed to own. The Anthropic and OpenAI Wall Street joint ventures from the same week become the second story when read against this one. Both labs partnered with Goldman, Blackstone, and Hellman & Friedman to "embed engineers inside mid-sized companies." Sierra does not need them. Sierra is already inside the Fortune 50. The labs are buying distribution because they cannot reach the customer the way Sierra already has. Look at who got hurt that nobody is writing about. Every enterprise software company whose roadmap assumed the data moat would protect the seat. Every CIO who told their CFO that Salesforce or ServiceNow would handle the agent transition. Every analyst at Gartner whose 2025 quadrant put the customer service #AI category inside the incumbents' magic ring. Sierra at $15.8 billion is the analyst report. The man who used to run the moat just priced it.