They aren't even close to a 1T company, they're valued at <400bb and that's at like a 20x-30x multiple. They can probably raise money at a higher valuation but its literally just value based on hype, not revenue.
https://www.businessinsider.com/anthropic-trillion-dollar-va...
Check the secondaries market ;-)
https://www.businessinsider.com/anthropic-trillion-dollar-va...