They're offering about $65Bn, of which about $1.8Bn is from existing stock holders. That's a tiny amount of shares from existing stock holders and probably not anyone who works at the company.

Wouldn't "by Anthropic" mean by the company itself - new shares to raise money? In that case the 23M shares being sold "by existing stockholders" would (might) include the founders, and seems surprisingly small ~1.7B at $75/share.

Maybe founders and employees aren't allowed to sell yet?

Why would the company get anything from someone else selling? It isn't the company's share.

The company is making a lot of money from the 800M shares they do own that they are selling.